As of today I would highly recommend bringing rock skis. You might want to check back on Friday though. They are predicting a foot or more of snow in the mountains tonight in the Bozeman/West Yellowstone area.
My coworkers that ski Big Sky say coverage is great on the mainstream groomer runs. There are steeps in the Lone Mountain Bowl off the Turkey Traverse with good coverage but you have to be careful. Challenger Chair is normal which means there are many ways down without hitting rocks but you need to know where you're going and don't ski where you don't see tracks. The tram is dicey on top especially the Otter Slide but the middle of Lenin, Marx & the Liberty Bowl have sufficient coverage once you're in them....just don't go venturing to the edges. Big Sky is huge so even though its doesn't have coverage everywhere you're still going to find tons of area to ski. If you're going to go exploring use rock skis until you know the terrain.
As for Bridger, the winds this past week have been a curse and blessing. Some areas like the North Bowl have had rocks covered up by blowing snow while the South Bowl has lost coverage. The groomers are sparse in some spots but skiable without doing any damage.
It is Big Sky, of course there are rocks. The traverses will be a bit sketchy and anything with lots of southern exposure(A-Z chutes). The heart of the runs are skiing fine. Marx, Lenin, Gullies, South Wall, Exit Chute, all that is fine. Just don't do mach 10 until you get into the heart of the slope. The Big is skiing pretty $$$$ right now as well.