Jesus Flores is in pieces, he still isn't able to physically throw a ball or swing a bat. Look for Pudge to be behind the plate as often as possible for the Nats. Flores is useless to you this season.
Zimmermann is expected to be out for a year and a half still, his career may have come to an end before it started.
Cut the Nats if you can't DL them, and even then don't let them hog the DL spots if you have someone else who needs them.
Yeah, Volquez is out for the year as well. I'm assuming you have lots of dl spots available, but I just don't see much worth keeping in Wiggy and Hairston. Hairston might be useful, considering how deep your league is. You could drop one of the Nats for him if he'd be valuable -- I just don't like dropping good players, even injured ones, for marginal talent guys.
Bottom line is none of them are worth keeping. I do 20 teamers every year, so I understand the depth of the league, but it's time to start looking through the scraps. None of those guys are going to be of much use to you.
D-Store, I think I agree with what you're saying, though it's really hard to. We have that external 60-day DL list and those players don't count towards our roster, so I think I may just name Volquez and Zimmermann as keepers and try to replace whoever I decide to drop in the draft. Their potential, if/when healthy, is too good to let someone else draft and DL them.