So you looking for an online service to do your job of filtering who you hire ? Don't be surprised if you don't get what you think you want.
If you're a dev company in any sense, it should be pretty straight forward to setup some kind of mock project that potentials can checkout and do something with.
Investigate the results.
If you want to know what they are to work with and what skills they have, then work them...and test some skills you know are needed for the job.
With that amount of revenue, you could easily outsource it to an offshore dev and claim back a lot of your time, while still retaining ownership of the app and IP.
If you're a dev company in any sense, it should be pretty straight forward to setup some kind of mock project that potentials can checkout and do something with. Investigate the results.
If you want to know what they are to work with and what skills they have, then work them...and test some skills you know are needed for the job.