Samtemdo8 said:
Was Batman even a part of that group or helped organized it?
As far as I can tell (my contact with the series is relatively recent), no. He was never a part of JLD.
The nature of Justice League Dark is that they face mostly paranormal threats. Some of the most well known members include Deadman, Constantine, Zatanna, Etrigan, Frankenstein, Swamp Thing and Raven. A man dressed as a bat would be so outclassed in these adventures as he is in most of his Justice League adventures... however, he is Batman, so of course he has to be included.