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

I can't say if you can run migration directly but hope you can. If not, it's still not that bad so don't be overly worried :-)

Worst case, you will have to use something like Disk Utility to restore one of the Time Machine snapshot folders to a volume (like an external drive) where it will look close enough like a bootable external drive.

From there you should have no issues using the Migration Assistant to migrate that old data (either directly from the Time Machine folder - or copied onto a hard drive) just like the migration assistant supports to migrate from an external drive.

In the past, I have been able to use Disk Utility to make a DMG file from a Time Machine folder and use Migration Assistant on 10.6 to migrate that data - but I haven't really tested it with Lion yet.

You will be able to do it with some time and spare cheap USB hard drive (or perhaps enough drive space for a whole image copy of one snapshot in time) - it's just a matter of how many steps and disk space are needed.