Do you have your owner's manual? That should tell you how to remove it.
If I'm reading your post correctly, the tail wheel doesn't pivot...but the wheel does turn, is that correct?
Anyway, per the Rhino manual (downloaded...if you don't have your manual, go to
this page and download Manual 00759048C), there is a pin the needs to be driven out. You see that pin atop the pivoting part of the tail wheel assembly.
I do expect you'll need some penetrating oil and perhaps something to drive that shaft out.
Since you can break it loose, then it binds up again, I suggest you look for any distortion or bending of that shaft.
If it's the wheel itself that doesn't turn...well, the manual doesn't go into that disassembly. That indicates the assembly isn't meant to be disassembled by the owner-operator. If you've any mechanical skills, you may figure out how to tear that assembly down. I would not be surprised if some of the components are pressed into place though.