Lets see, lets see....
First off it is a dog and very likely to have a high base speed. If you can chase down scouts, even if you use rocket boosts, you have a speed greater then theirs. This makes the scouts speed bonus, the core of that class, obsolete. Given that you have the same health as a scout, speed of a scout and higher fire power of a scout you now become more powerful then that whole class.
The primary weapon is on par or just a little lower then the heavies weapon being a massive fire rate which is a benefit only the heavy should hold. I can only judge by pictures here but it seems likely that it doesn't have the slow down effect and when coupled with a faster base speed could easily make this weapon more useful then the heavies main, which is the heavies core advantage.
These two alone have made two classes in the game weaker. Rolling these elements into a single class ensures that the two in question will be loose their uniqueness which allows them to better fill the niche they are meant to be filling. Oh and it won't matter you don't have as much health as the heavy at that point. Speed can be better, used right, then health ever could be if you can hit their flanks fast and hard. I am giving away part of my trade secrets as a combat engineer in that bit of wisdom.
Your secondary weapon could actually play a interesting part into the game but it further weakens the medic which has already taken a small blow by the heavy dropping sandwich. Unlike the heavies sandwich, which is the equivalent of a pill bottle, the dog will be able to drop a super sized medkit. To use the same step up I mentioned below, yeah I am strange and write posts in all sorts of order, added with the faster speed and fire power this carrying 'weapon' makes you more combat efficient then the medic which eliminates the largest down side of working with a medic: He is incapable of defending himself or assisting you while he is healing you.
This doesn't even touch on the metal aspect which looks interesting at first glance but would make engineers like me a little too strong if used well. You could argue that two engineers can be good together, and yes they can, but they don't eliminate each others weaknesses to a great extent. They are still only moderate in defensive fire-power, speed and health. This K9 unit, though I am assuming you can drop the metal your carrying and pull out a gun, means the engineer has faster, heavier hitting, help yet still doesn't loose the build a gun to level two capacity.
Rocket boosted melee also over powers the characters melee but if properly balanced it would actually be a benefit they should have. I can understand why they would want to do it this way. Dogs are a melee based creature, seeing they haven't opposable thumbs, so you would want a benefit to the melee to try and make this their primary method of attack. I think it having a strong melee and a way to get in fast and furious should be the niche it is striving for so I won't fault this heavily.
The skill? I have to give them some credit for not just suggesting you have the ability to detect spies, completely obsolescing a whole class. Still if used correctly, and very likely it will be the primary use of this ability, it will seriously damage the spies class. After all you don't really need to know where the other classes are, snipers are going to be where range benfits them the most. Engineers will be in more defensive choke points. Heavies will stick with medics and likely try to become the front line... and so forth. Spies... spies try to get behind you, they are the ones to watch.
Overall this class weakens the standing of: Scout, Heavy, Pyro, Medic and Spy. Yet the biggest 'balance' factor of this game has been making classes useless outside of their niche as I have said. This is over all a fast moving, moderate to high damaging, high fire-rate, moderately healthy class capable of a few unique tricks. Those 'stats' alone make it better then all the other classes without throwing in the two special abilities it has (tracking and ammo/heath carrying) to further tip the balance. Other words: it is capable of operating far more effectively out of the desired role then any other class.
There are a few good ideas in this class but it needs work to make it plausible for the game setting... If I had to make a suggestion on this class:
Replace the primary weapon with a form of bark attack. I was thinking stun but that would make you too powerful indeed, but maybe a slowing effect could give a good balance. This classes niche should be a heavy and fast melee attack. Removing all real range ability would force it into this position better then what it is now.
Lower the health a little, a frontal attack with this class should be suicide. Force them to use the benefit of a higher base speed coupled with 'rocket powered' lunge attacks to strike from the back and flanks. It is after all the tactic used most by canines you know, worry a enemy from the flanks and rear and then retreat while your pack mates with guns hit them as they turn to deal with you.
The skill needs tweaking too, but the suggestions I keep thinking on are all... well too much of a under-power. Then I am over balancing into the over-powered spectrum with anything I come up to make it even more useful. I do know one thing, water should be able to 'shake off' the pursuit of the canine somehow.