It depends. If the individuals qualify, per the program rules, then sure they could be selected. That said, one of the points of GSoC is to get more people introduced to open source and picking someone already integrally involved is a lost opportunity. So depending on the exact specific situation and eligibility, it could be allowed and frowned upon, perfectly reasonable, or in violation of terms.
If you feel someone or some org is in violation of the program rules, you could report it to
gsoc-s...@google.com
Cheers!
Sean