I've never owned an ATV/UTV, so all that I am going on is second hand from my son, who is a mechanic at a Honda Power Sports dealership.
He tells me the thing that kills ATV/UTV drivetrains more than anything else is lack of maintenance. He says that for some reason, owners seem to think that they can drive these machines in the harshest of conditions, and neglect filter and fluid changes.
Considering this, I would suspect that frequency of oil changes on a side by side would be much more important than exact viscosity being called for. But Polaris machines tend to need more maintenance than most others, so perhaps using what they call for could be important.