It's almost like a relationship question, but can SCS pets be mates with adopts that aren't from SCS but of course, not breed?

You are correct, SCS pets can be mates with non-SCS pets and just not be able to breed.
Only SCS pets may breed with other SCS pets; if you see anyone trying to breed their SCS animal anywhere but the SCS nursery, it'd be best to let us know so we can notify the user :" > Thanks for asking the question, its a good one!