I'd go all STR. The bar is extremely low for these dungeons.

Learning to keep threat can be challenging if you don't have experience with it, but most dungeons are extremely forgiving for tanks otherwise. Heck you don't even really need a tank for many of them.

The only thing I can think of where the extra VIT could benefit you, is possibly taking overlapping AoEs. If you're skilled enough to recognize that standing several overlapping AoE markers could really hurt and can successfully avoid them, id say go STR.