Yes, it is a common spammer technique, but we at HBT are pretty good at deleting those posts before they go live. Our methods aren't perfect however.Take a look at this thread on another XenForo forum that I am a member of.
I'm not saying that everyone who joins and then resurrects a zombie thread is a spammer, but it seems this is a common strategy for spammers to slip in unwanted links.
doug293cz