Ok I can understand that you shouldn't be able to sacrifice a good creature to obtain a good supplicant. But there's no reason why you shouldn't be able to sacrifice an evil supplicant for an evil creature.
To balance things out, a change could be made whereby evil supplicants are predisposed to attack good mobs that are at least half their level. In other words, your pet imp simply cant resist attacking any little peasants or kittens that it runs across. Also, the sashes should attack evil supplicants on sight. Why would the sashes autoattack kobold mercs, but not see any problem with disgusting evil little supplicants running around town?
I think this would be a fun change and would not be too much of a discouragement for people to summon evil supplicants.
-Juggleblood