It's been done in other games and I Think it could be fun. Eq2 model is good one as you had to collect an item usually as random loot to be able to place a certain type of mob in your dungeon.

I Think it would be better to make a new Set of achievements. Maybe kill 1000 wolves and reward is to be able to place wolves in dungeons you create. Have a rating system and a report system all mobs drop from a loot table which is based on Mobs levels. Reports for that guy who places a sing lvl 67 mob so he can farm something safely. Also this would Greatly increase content for players who grow tiered of the dungeons they do over and over.