Would they be stripped? The traditional alias separator is a '+' (dijit+hackernews@google.com) and periods are part of email names, thus the address itself: (jan.harasym@google.com)
Well, I've gotten spam that had it stripped; the name was a bogus one that I gave out in combination with a specific dot-aliased address, but the address in the To: header was without the alias. I can't say how often it happens, but with major mail providers (including Google, IIRC) widely known to support arbitrary dot aliases for throwaway addressing, it seems like a reasonable ploy from the spammer's point of view.
Google definitely do not support dot aliasing, I've had email addresses for gmail with dots in them and so has my mother. Thats dangerous if you allow people to sign up for email addresses with dots and then use that as an alias seperator. So dangerous I would argue they wouldn't do it.
Gmail explicitly ignores dots in email usernames[1].