Teenager, my take on frum kids involvement in these organizations is that, except for the rare exceptions, either the kids don’t get involved till they are mentor-age, or they should be in the majority. My kids were involved in a wonderful chesed organization that included some less observant girls (strictly not coed BTW) and they gained a lot from working together for a common cause. But once the demographics shifted and the non O girls were in the majority, I wasn’t comfortable with my kids getting involved, definitely not while still in H.S.
Back in the 70s I did have a few friends from my BY class in NCSY but they were in the exception category due to circumstances that aren’t relevant here.
Oh, and it should be understood that going into it with a strong identity and convictions will help to not be influenced. Again, I don’t think that NCSY is in a position to absorb all the kids that could benefit from such an organization. Some, but not all. Which gets us back to square one – how to design and promote an NCSY for OTD kids.