Countless numbers of RV's on the road with rubber, tpo, etc - soft material roofs, with absolutely no issues. Some folks will tell you it absolutely has to be fiberglass and I say BS. Fiberglass roofs have their share of issues as well. The roof material would not be a deal breaker unless there was a specific issue about that particular roof (like the winnies with fiberglass seams and the roofs pulling off from lack of maintenance)
So no, the type of roof would not be an issue for me. The condition of the roof is. And I don't care what kind of roof you have, failure points are very seldom the material itself and more about all the holes in them from various things, like AC, vents, cap seams etc. And all roofs, no matter the material, have that.