I have introduced large numbers of spotfins to a pond with a heavy smallmouth population; they seem to be doing great and are clearly recruiting. I wouldn't worry about the perch being able to put a dent in their population--they are extremely quick and active, and only when they are first placed in the pond do they seem to be especially vulnerable to predators.

I have found that putting them in the pond right at dark, and stocking from a black bucket, can really reduce losses. If you keep them in a white bucket, they are quite light colored when they go in the pond, and really stand out. Coming out of a black bucket, they're very dark and blend in immediately.