I have never tried it but I know people who have fostered baby goats on sheep mommas so I suspect it will be just fine. Sheep's milk is richer than either goat or cow so I bet they will be very fat and happy goats.
If you think they'll get fat on sheep's milk, try feeding Jersey colostrum!
Are you talking actual sheep's milk or milk replacer. Real milk would be fine, but I'd stick with kid MR over lamb MR.
Our bottle lambs and kids did really well on a mixture of goat milk and Jersey milk, some sheep's milk and lamb MR to stretch it out (there were a lot of mouths to feed).
Do they milk their sheep? Generally speaking, when folks milk sheep it is to make cheese instead of for drinking. Sheep also produce less milk than a goat or a cow so the milk could be more expensive.
Personally, If I didn't have access to raw goats milk, I'd find someone with cows and buy raw milk off of them.
We only added sheep's milk to what our lambs/kids were getting because we had 3 ewes that gave birth and had milk, but weren't raising lambs for various reasons.