If not, is there a good way to use TKinter with the ported Python?
No, ported version of Python doesn’t support TKinter. How are you going to use gui package on USS?
It would also be nice to be able to use the Python IDLE IDE via X Window System from a remote terminal using e.g. MobaXterm rather than connecting with a line mode terminal to a line mode Python on USS.
z/OS USS seems to support X Window System
Advantage would be: display of Unicode characters
That is rather a decision for development management …