I've not seen one on a hip, but our lab had one under his "armpit." It was a pretty sizable lump (about a pea but large enough to be noticed). He didn't seem to be in pain when I touched it.
It started to go down after a few days, but we took him in. The vet wasn't concerned about it - thought it might have been a bug bite since nothing else was bothering him.
I'd still take your pup in - better to be safe than sorry.