If you don't have a Tapastic account, you can't look at anything that's marked NSFW. It prompts you to sign up instead of actually showing you the page when you click "show me."
The question here is how to include nudity in a way that it DOESN'T have to be behind the NSFW filter, so that people without a Tapastic account can still look at it.
As far as the actual question, honestly I'd say that if you have a significant audience that's not on Tapastic, it might be worth it to mirror on another site, even if it's just making a tumblr dedicated to your comic or something, so that they don't have to worry about it.
I'm not staff so I don't actually know, but I feel like there'd probably be a little bit of a Spirt Of The Law thing here, to be honest -- like, if you have a character who's technically naked, but she's standing behind something so we only see her from the shoulders up, or she has a sheet creatively draped around her so we don't really "see anything," or a guy who's naked but standing behind a couch or whatever... like, that's a normal comedy thing and I feel like that'd be fine. But if you have a seductive image with a thin black bar over juuust the nipples and go "TECHNICALLY NO NIPPLES SHOWING, ITS SFW" that, uh, might not be in the intended spirit of the rules?