I have owned both for a while now.
Design wise they are both very good, and very simlar. The edge geometry-profiles are nearly identicle. It is in the construction, the fit and finish that they differ. The Sebbie just fits together so well it makes you want that in every folder you own. The titanium on the Dominator is a bit thinner it seems, and has a different texture that seems to resist scratching. It also has a much more ergonomic handle and the flipper makes it much less likely for your hand to slip onto the blade.
Neether of mine have any bladeplay, but when I tighten the Dom to the point where the lock is solid, the action is slower and harder to deploy with the assist. Also it is not quite centered in the handle no matter wich technique I use to reassembl it. The other problem I had was the pivot pin being stripped when I got it. I transplanted another from my Cuda Maxx and now it is fine.
The Sebenza's lockup is infalible, its blade is always centered, and it can be easily taken apart and ressembled without unreasonable concern of ruining its perfect fit. The titanium feels softer, more comfy to me....scratches a bit easier, but still not bad at all. My sebbie is BG42, I perfer S30v (on my Dom and Strider AR) but BG 42 is very very not-bad.
As far as service I havent had to send in the Seb for anything. I have had some probs with my cammilus folders, and Will Fennel and his crew are great people to deal with. And they love knives, which always makes me happy. I consider there service very good.
I would say the Sebbenza is without a doubt worth the extra dough. Its simplicity, functionality, durability, and impeccible construction are all above even the high quality Cammilus Dominator.