There's allegedly (it's an old issue) currently a crash issue when used with Cubic Chunks, which you can find here.

This issue could very easily be solved simply by having an option in the config to turn off all mob spawning, without disabling the mobs themselves. Then I could use Vertical Spawn Control (a mod that lets me customize mob spawning) to handle primitive mobs.

Obviously fixing the problem with cubic chunks would be better, but this simple config option would do just the same and I would guess that it would probably take a hundredth of the effort, which means I could use this mod on my server sooner.

If this is already fixed with cubic chunks, then this issue can just be closed, but I've not heard or seen anything mentioning it being fixed.

Update - I tried it, and it didn't work. The flame spewers are in the registry for each biome, but I haven't seen a single one spawn in the nether's lava sea. This is a pretty big bug.

Looking at my entity output for biome tweaker mobs I've disabled still are showing up in the output for entities. I haven't done it yet but I was planning on turning off the flame spewer and putting them back in using entity ID and BiomeTweaker with a lower spawn value.

I can't say for sure my plan will work but if it does I don't see any reason why you couldn't do the same thing using cubic chunks. It certainly appears as if the entity is still being registered.