you can shoot skeet and trap just fine with a pump, but its going to take a little extra practice to be able to do it as well as someone with an O/U or a semi auto.
I have a pump and can shoot three hand thrown targets and some people can shoot more. the world record i believe is 9 clays with a pump, but of course that is by Tom Knapp himself.
ps- this is with a stock mossberg 500 20 gauge. with a shotgun it doesnt matter how much it costs as long as it is reliable and you can shoot it quickly and it fits you well. practice is more important than anything.
I would bet on a guy who practiced every week with a lousy old beat up shotgun that a guy who practiced once a month with a really fancy $5k O/U... practice makes perfect.