Is resilient channel appropriate for sound isolation?

I don't spec resilient channel. The fact is, there is no single standard for its construction. Some is 20 gauge, some 25, some in between. Some are slotted for flex, some are solid, some have holes.

Resilient channel isn't a reliable choice

The design of the channel is not standardized. Not something we can count on. Also, it is likely (statistically) that some of it will be installed incorrectly.

Again, there isn't a standard for strength or flexibility. Drywall furring channel, on the other hand, is specified by the Steel Stud Manufacturers Association, along with all other steel framing components.

This method of decoupling is effective if the steel can act like a spring. Since there's no manufacturing standard, the net result is that you have no idea if the resilient channel is too stiff (no spring) or too loose (no spring).

Much better to use resilient sound clips and Drywall Furring Channel. For a low cost solution you can install a ceiling with these steel clips + channel that would put any resilient channel ceiling to shame.