Heh, glad you're enjoying the Shadow Summoner :)
Now, it's been a long, long, LONG time since I've poked around the ENTs, but if I'm remembering correctly, spewers can only handle ten different entities to spew. If you want to have more than that, you can set up nested spewers. Say you want to have a spewer pick from 14 entities to spew. You'd set up two spewers that each pick from seven of the entities you want to spew, then you'd make another spewer that would call one of those two spewers.
Again, it's been a long time since I've done any TM modding, but I think that was a solution that would work.