Any type of mule will make excellent ewes. What you have to remember though is that mules are the sheep equivalent of a high yielding holstein dairy cow. They only perform well if you look after them well. Also they will only last about 3 to 4 seasons realistically.
As for lambing mules outdoors you will have to be careful about which tup you use as the lambs may not be very hardy. It's a job to balance hardiness with performance. i.e. a texel x lamb will be hardier than a charolais x but texels tend to need more assistance at lambing.
We have stopped keeping mules now as they are very high maintenance. We now have easycares which are virtually trouble free, though not quite as productive. Well worth a try in my opinion.