I just noticed there won't be a Sat swim clinic offered for this year's DC Tri. Do you know if we're allowed to get in on our own to feel out the course?

You're generally not allowed to swim in the Potomac River unless a group has received permission for a specific event. Based on the comment on the official WDC Tri Facebook page about open water swim practices in the DC area, I wouldn't count on swimming the race course on Saturday.

You can still walk down there and scan the shore for good landmarks to use for sighting. It's not quite the same as swimming in the river but it's probably all you'll be able to do on Saturday.