I don't see the draw of OSE and C&C is AD&D 3e.
As for compatibility issues in the OSR, I see lots of number counting of angels on the heads of pins. Back in the day, it was very common to mix and match B/X, AD&D, Arduin, Judges Guild and whatever weird zine you picked up at a local con.
B/X has always resounded with lots of gamers, so no surprise that OSE would gather fans. Of course, the joke of OD&D has always been that when you take 0e and add piles of new stuff, you end up with 1e and now need to go find 0e again.