I dont know of anybody who has gone straight from ACC to any legacy carrier or SWA, although many have tried. If anybody tries to tell you that ACC is the fast track to working for UPS, dont believe them. Many have tried this, I know of only one guy who managed to get an interview, and he was there 5+ years, in the SDF hub everynight. A couple of guys have gone from ACC to FedEx, but they had major internal recomendations. Working at ACC had no effect on them getting hired there.
I'm one of those guys that have managed to get a decent job straight from the Shorts. In retrospect i probably would have preferred going to a regional when I was an F.o but at the time no regionals were hiring. It worked for me but it was a long time coming and yes I was one of those guys who loaded near 7000#s of freight by hand in their uniform every night.
Absolutely don't think working there will help you get on at UPS. There was rumors of a flow through from management years ago but make of that what you will. A lot of guys form a genuine disillusionment with boxes and UPS (ask any former feeder pilot how difficult it is flying as a feeder for brown) and would probably stack shelves before applying there.
I guess a year out of your life isn't bad (1yr training contract) and it is good flying experience, so if you are at around the 500tt mark you could probably do a lot worse than to fly the old box for a while. I guarantee when you get a real job you'll still be telling stories from your freight days.