powder coating and bearing survival

Has anyone powder coated a swing arm and left the swing arm needle bearings in?

no, if you make sure there is no rubber, you could get away with it but they would have to be cleaned meticulously other wise any grease remaining will melt and run over your new paint to clean them I rekon you will need to press them out..

Here's my two cents, remove the seals then put a wad of paper in the centre of the needles then silicone both ends shut, the sandblasting won't get through the silicone so shouldn't get any media in it.

And the silicone is not gunna melt in the oven. When you get it back a screwdriver through the silicone and remove the plug.
But of a clean with a blade and should be good to go.

P.s. Did I say silicone?

By the time you have done all that it would be easier to just remove the bearings and fit new ones after ! I have done several frames and engines over the years and (trust me) the blasting media will find it's way in there.
Usual saying ..... do it right, do it once

Try nut and bolt through centre with washers sealing it off

I will add that if you have the correct bearing driver, you should be able to push them out and re-use. I would agree with others that by the time you do the alternative, you could have had the bearings out. With the proper bearing driver and a vise, its a 1 minute job.

Ok guys, thanks. The powder coating shop seals everything off real well. I was more concerned about the heat from the powder coating ruining the needle bearings. But everybody's right, it would be best just to remove them, which I have to take them to a shop to do, and then install the same or new ones.

a socket and vice with a bit of wd 40 usually does it (except for those pesky ktm ones that only go one way)