Looking through EnderZoo.cfg and SpawnConfig_Core.xml I wasn't able to find a way to disable or change the spawn chance for the Khndrel Keght (the mob that randomly spawns when dirt is broken.)
Please add a config option, or if it is already available, add comments or sample settings to disable or change the spawn chance for this mob.

If I recall, it's called Dire Slime in the configs

You can either set direSlimeEnabled to false or set their span chance to 0 (recommended).