Can I restore a Snow Leopard backup onto a Lion machine?
It's not complicated at all. I can't point to a current Lion Apple support doc but I just moved my old snow leopard time machine backup to my new Lion install.

Simply launch Migration Assistant, select your Time Machine backup and select which settings and users to copy. It doesn't care that your backup is a Snow Leopard backup.

For more information here is an article about how to use Migration Assistant in Snow Leopard. It is virtually the same in Lion.

http://docs.info.apple.com/article.html?path=Mac/10.6/en/27921.html