The problem with Andy playing doubles at a Masters event is that it could interfere with his singles concentration.
I believe that Andy is doing it firstly to help Jamie's doubles level and secondly to ensure that he will be picked for DC and the Olympics partnering his brother.
But it also gives him some time on court before the singles (assuming he has a bye) which is no bad thing given he's not played competitive tennis since DC. I hope he won't do it at Cincinatti as well given the conditions there but I think it's a good idea here. And I like him playing doubles because it gives him more practice at the net. So I'm ok about it in this context.