I think it'd be fine to soak your bits in Simple Green - just be sure
to lube them with router bit bearing lube or something else appropriate
as soon as they dry. If you're trying to get pitch off the blades, I
don't think Simple Green (a degreaser, right?) would be the most
effective solvent - I'd get some blade/bit cleaner and wipe off the
blades, and leave the lubricant in the bearings. Not worth going cheap
on tool maintainence if you have lots of money in the tools already.
Let us know what works,
Andy