I've never heard of a dealership sucking the oil out (we don't do that at the dealer I work at, they just short the lube techs on labor to make up for it, don't ask how that's smart...) but I have heard of places like Jiffy Lube and such being caught doing that.
Chances are they might have skipped the filter element, I'd hate to say it but the way dealers pay technicians (i.e. they cut the labor time paid to the tech to way too low) I wouldn't be surprised if some techs just skipped the filter element, most people wouldn't even notice.
But how do you know the skid plate wasn't removed? Also, if you're 100% sure they skipped the filter, I'd just take it back and confront them about it. As for the oil drips? Like I said there's a lot of pressure to get those oil changes done fast (service writers not spacing RO's apart enough, unrealistic deadlines, lazy techs, ect ect.)
I'm not trying to justify the dealer's actions or their techs, I'm just saying from my experience; dealerships can make even the best of technicans lazy and shortcutters just to make a decent pay check. The dealer pay structure and how they treat the techs often is pretty crappy and after a while even the most honest tech starts cutting corners to make a living. That being said, a lot of dealers are also pretty crappy to begin with...