This may apply to owners of other brand tractors so I'm posting it here as well as the Kioti forum.
This is the factory reply to my question as to why rear fluid couldn't be used in the front axle rather than gear oil as the manual suggested.
Why??..Well it appears to have come from the factory with fluid in the front diff. and also why not keep down the lube inventory?...Here's what they had to say:

The DK 40 rear axle is lubricated with the fluid from the transmission. It
is acceptable to use the same hydraulic fluid that lubricates the
transmission and final drives, in the front axle. It is also correct to use
80-90w gear oil, as long as all the fluid is drained from the front axle and
the oils are not mixed. Be careful that you don't alternate the type of oil
used. If you decide to continue using the same fluid that is in the
transmission stick with that oil. Thank you for your questions and concerns.
I hope that you enjoy the use of your Kioti Tractor.

Best Regards,
Allen Clemmons
Assistant Service Engineer
Kioti Tractor