The scheme distributions I'm familiar with (Chicken, Gambit, and Gerbil) have well-defined FFIs for C.

I think with Gambit you can have C inline with your Scheme:

https://www.iro.umontreal.ca/~gambit/doc/gambit.html#C_002di...

This is no help for programming for embedded targets? Maybe? I'm very close to clueless (I RTFM, but I still don't understand a large portion of functionality of Schemes of FFIs).