Since 5.1.1 is the first release which allows simple ring yes.
Now when 5.1.2 comes out it shouldn't be a problem, but this is not something I have tested.
The difference in 5.1.1 and earlier releases is the ability to configure L2 fabric, the underlying architecture is different, and we have an updated satellite control protocol. All of these allow for topologies such as simple ring.
In the future with newer topologies if the underlying architecture changes enough, or the control protocol goes through a major revision then it is possible you would see an issue, but I don't see it being an issue with the next few releases.
HTH,
Sam