I've always waitressed in the summer while doing base, but as a girl I do 50-70 mpw in the summer, so if you're a guy you might of course be running much more which would be tougher. It's tiring for sure, but doable during the summer months.
It REALLY helps if you work days as opposed to nights - you can fit in a morning run, go to work, run after work. Just like any other active job. But then I always do my major runs in the evenings. Even if you're more of a morning runner, though, working nights would suck and it can be hard to avoid taking those shifts in the restaurant industry.