Ryuzaki said:
They do not spit acid, that implant organ is generally not used. I actually don't know any chapter that uses it. They do have implants that allow them to resist almost any poison; others that allow there blood to clot almost instantly to any wound, a reinforced skeleton, an implant that allows there armour to become a second skin and a few more implants or genetic enhancements that I can't remember.
If you're taking about Chaos Marines, then it's quite likely that some of them do, but it sounds like your just taking about loyalist marines.
All Space Marines have that ability, including Chaos Marines. To quote from the Lexicanum:
"Phase 17 - Betcher's Gland - Consists of two identical glands, implanted either into the lower lip, alongside the salivary glands or into the hard palette. The gland works in a similar way to the poison gland of venomous reptiles by synthesizing and storing deadly poison, which the Marines themselves are immune to due to the gland's presence. This allows a Space Marine to spit a blinding contact poison, which is also corrosive enough to eat through iron bars."
For the full article, see http://wh40k.lexicanum.com/wiki/Gene-seed
As for chapters who actively use the gland, the Iron Snakes come to mind. On their homeworld of Ithaka the brothers of the phratry frequently conduct trials and exercise regimen with the new initiates, and should one of them be bitten by a poisonous snake this is looked upon as a good omen; the oolitic kidney filters the toxin out of the bloodstream, while the Betcher's gland converts and stores the toxin for later use. Just read 'Brothers of the Snake', it's Abnett anyway so you won't be disappointed - I found it to be a good read.
As you might have guessed by the sheer nerdiness of the post so far, W40k FTW.