I just done some extensive searchs on the net and found that it seems common for a lot of people to run primed brass through a feeder with no problems. While I've never done this I would say go ahead but only at your own risk and not mine.
Just do a google search - primed brass case feeder - and you'll read some of the same articles.
I agree, I run the LNL with a case feeder and use primed rifle brass as I like to hand prime it to get a "feel" for any soft primer pockets. It's not the case feeders that worry me, it's primer feed tubes that I pay close attention to.
I made a long thin follower out of stainless stock with a red flag on top that follows the primer level down, it lets you see there's only a few left in the brass supply tube as it bottoms the flag out on top of the large round outer tube wall before it runs empty.