I have not seen Donald at Chef Mickey's but have been given the impression he does turn up. I've been there 3 times and it was always Minnie, Mickey, Chip, Dale, Goofy and Pluto, which is a lot of characters for your money!
We found it very hard to track down Donald in 2003, we never found him..we just missed him on the Epcot bus thing. It was a personal quest last year!!! We found him on the Epcot holiday bus 2004...the amount of times we ran into Goofy and Mickey, but Donald was a real enigma. So check the times at Epcot for the Disney Characters On Holiday bus, he is not on every one, but try a couple of times and you might get lucky! I have never seen him anywhere else but Epcot, even in the distance (other than parades) He does turn up elsewhere, but I guess not if he knows I'm about!
I've enjoyed character meals before I had children, it's still pretty fun. We are going to Breakfastasaurus this next trip, the character to guest ratio is pretty poor compared to the other character dining options, plus I have heard some less than favourable reviews of the food...but you don't know until you try, my DS4 will probably enjoy it regardless. I also get a Donald sighting without the hassle..my character mission for this year?? Mulan!!