Why can't you use the angelic set? 50 dex is only going to add around 400 base ar to your build, which isn't really worth it imho. Like I said though, grand charms can add something like 160 ar each, small shave 20, daemon limb can increase it by a good 4k or so, depending on your gear and base ar, and then items like angelic, metalgrid, ravenfrost, and arreat's face all add a ton (angelic adds 13,000 ar to my barb). Plus, your weapon already has -25% target defense, which is pretty nice.
Also remember that chance to hit is also based on monster lvl v character level, so as you get bigger, the chance increases. Some things, like baal and such, you'll probably never have a 90% chance to hit anyways though, so don't fret it too much.
If you're that scared of dex, go ahead and pump it up some; there are just more efficient ways of getting ar. I believe the last time I built a BotD tmaul barb, he had no dex and was hitting around 7-8k ar, and this was with no charms, no angelic set items, and before I knew about Demon Limb.
If I get a chance tonight, I'll run one through the loader to seethe actual % chances and such with base dex, though I have a lot of work tonight, so I might not be able to. I'll try though!
-Hal