yup, those tires are all right. 140/90/15 fits fine. Probably the most common size rear tire people run. (Stock is an oddball 140/80/15 - too hard to find. )
you can put a "tubeless" tire on our rim, you just need to use a tube .
(I have put 4 or 5 "tubeless" 140/90/15 rear tires on my '07 since the stock tire wore out)
If you have Dunlops on there now, check and see what size they are. I think a lot of guys run D404s and 140-90 is probably as close as you can get.
best practice is to get a new tube too, though i have reused tubes without incident
rebeats are fine, but i'd stay away from retreads