Yeah, any standard 802.3af PoE injector will work with your R500/R600/R700. I've used numerous injectors with different brands, including the cheap ones off Amazon, and they've all powered Ruckus AP's without a hitch.
The only gotcha is that if you have a Ruckus R710 and need 802.3at PoE+ mode, some vendors misleadingly sell "PoE+ injectors". Ruckus AP's won't detect those as PoE+. But, obviously, there's very very little that you're missing with the R710 if you use PoE compatibility mode and I wouldn't worry about it.