I do believe that mo'creatures is still going strong, but was on a hiatus for a while.
It IS currently updated for 1.1.0, however I read in the FAQ that he is not allowing it to be a part of mod packs... I'm not sure if tekkit would be considered a mod pack or not, but ... Here's the link: http://www.minecraftforum.net/topic/81771-v110-mo-creatures-v322-with-goats-jellyfish-mantarays-and-stingrays/
It would be really nice to see this in tekkit, but I would understand if it's not possible.