Hi all.
From what I understand, the Rangifer tarandus on exhibit in the Tundra Trek will be European reindeer (the ones on display in Eurasia right now). As you may remember from earlier this spring, the zoo has enough trouble maintaining one subspecies of reindeer, let alone doing so with another subspecies (in an exhibit right next door).
As for the musk ox, I think the plan may be to close the domain once the North Site has been redeveloped, or at least change it into more of a nature walk, rendering the current exhibit useless (or, if not, there are bison currently off exhibit that could use it as a home). At one point the zoo had a rather large herd of musk oxen (8+), and bred the species on many occasions (the current male was born at the zoo).
To my knowledge, musk oxen and caribou were never exhibited together at the zoo. (The caribou were initially only visible from the monorail, and for a time were on display in what is now the moose exhibit). During the (initial) design of the tundra, the musk ox / reindeer area had to be subdivided to ensure that the species could be separated should the mix not work out. (Musk oxen are not the nicest of animals ... or the easiest to keep ... the current male fatally gored at least one female). The fact that the most recent plans show only a single space strongly suggests that musk oxen are out (sorry!).