I don’t think it makes any sense to use an OSSC with a RasPi.
The purpose of the OSSC is to digitize and line-double/-triple/etc. the low-resolution, analog video signals of (primarily) old game consoles that newer TVs can’t handle for one reason or another–lack of appropriate analog inputs or 240p support over HDMI on the TV, and/or lack of HDMI support on the console.
The RasPi boards all come with digital video output over HDMI, so they don’t have the problem that the OSSC is intended to solve; not to mention you’d be spending an extra ~$250USD’s worth of equipment to degrade your signal by converting from digital to analog and back to digital. :/