I used to always say no to this
But the other day I found out a friend of mine did it...though he was an AE capt before UPS. I know another guy who was a part time ground manager while on furlough from Air Wisconson in the 80's (I think) then got on with UPS.
All in all, I wouldn't go out of my way to get a job throwing boxes to work for UPS since you'll have to be way qualified in other areas...including a pilot recommendation(s). I don't think they would lower their quals just cause a guy threw boxes...on the other hand, it couldn't hurt to have such a thing on your resume. So, if you have time on your hands and want to do the job...go for it.