I see no reason to disallow it. Some rss crawlers might pick up on it too, possibly bringing you more traffic.
I always disallow search engines for my feeds. Search engine crawlers have no business there. I also do not link to my feed directly...I remember a time when this messed up Google. That was long ago, but who knows what crazy search engines are out there. Save the traffic and keep the bots out. You get traffic from pinging, not crawling.