The 2008 rear spoiler is "incorporated" in the trunk lid and has the 3rd brake light as well. I don't see any way you could add an '05-'07 rear spoiler to the '08 and make it look good without loss of the 3rd brake light function.
I also agree those gaps look wide, but it may be more of the angle of the shot. For example, it would imply a very narrow gap on the driver's side. Either way, those gaps are/should be adjustable and could be tighted up.
Is anyone making spoilers for the 08's that have a cut out so the brake light shows through. I bet there's going to be alot of people looking for that, because I think the small SRT8 05-07 spoilers were very popular. If anyone finds what I and others are looking for (small spoiler like 07's, w/ cutout for 08 brake lights) if you could please post the source, it would be much appreciated.