you could probably handle the siege (first four bosses) and antechambers (next three bosses) of uld. you could probably OT some stuff for freya or thorim, but i dont know about MTing either of those, or MTing for hodir/mimiron. if you have a frost resist set, then you can OT for hodir when he gains icy blows.
vezax and yogg are a bit tougher. the tank i run with in 10 man tops 50k life raid buffed (unholy tank dk). the feral OT we run with typically tops out around 47k or so.
but by the time you snag a few pieces off of the first 7 bosses, you should have had enough of an increase to tank the keepers, and shortly after that you could probably do yogg and general without too much trouble. do yourself a favor and get a dps offspec tho, because some fights in uld (i.e. general) just dont need more than one tank.
also, dont be afraid to start out with 10-man uld either. most of the fights in uld have a lot of **** going on with them, and most of it is that stuff you cant get used too unless you see it in action (videos help too).