Can I delete Lion and re-install Snow Leopard while keeping my Boot Camp partition?
Yes - the Macintosh installer only touches data within the partition when re-installing Snow Leopard, but there's no guarantee the windows software will still start since Apple doesn't support going backwards like that. (i.e. they don't test it so you have even less support that what they provide for Boot Camp in general)

You may have issues on the Boot Camp side if the older Boot Camp software sees that your boot camp partition is newer than it expects. This means it may not work, so you need to be backed up and prepared to reinstall the Windows side of things unless someone else can edit or answer that they have tested this out several times. It might be fine, but I would feel bad if you took the Mac side being easy as assurance that everything would work perfectly on the Windows side after you go backwards.

The prudent thing would be to install Snow Leopard onto an external drive and swap that inside the mac to test whether Boot Camp will work on your new setup. This involves time and potentially tech money, so you might want to check into virtualization costs if that is a viable alternative to you.