You lack UMD, or stealth, or even Tumble to help get into a flank with (though I guess swapping Ride for it is an option), is what I mean.

Ok, that wording is strange. Thug gives up the 1st level bonus feat, and SA fighter replaces all bonus feats. They should not be stackable... Not sure what takes priority, the fluff text or the actual mechanical changes....

Even if they do stack, I'd much rather do Dungeoncrasher Zhentarim Drow Fighter. It is a nice trick, if doing SA variant anyway, to trade the feat you already gave up anyway for Thug, though.