Short answer: Not until it's ported to Bukkit
Last time I looked, Mo Creatures had a buggy SMP, but not Bukkit support. You'll need to wait for / request someone to port it to Bukkit before it will work with Tekkit.
Even then you'll probably have to wait until the next Tekkit release, unless someone is willing to also port it to the older Minecraft / Bukkit versions that tekkit is using.
If you're not afraid of some effort, you could instead manually mod a vanilla 1.2.5 server with pretty much all of the Tekkit mods. You could even add in others, like Mystcraft, if you like. You also have to mod your own client. Not exactly easy, but satisfying, and you get your server exactly how you want it.