I could not find any final conclusion about the compatibility URC MX and Lutron MAESTRO RF. Lutron introduced a version 2 for their Maestro- RF2 series last year, May '09 :
MRF2-600M (dimmer incandescent lights ), MRF2-6MLV ( dimmer low voltage magnetic lights ) and MRF2-6ans ( switch ).

- do these new products from Lutron work with MX ( I have a MX-6000/PSX-2/MRF-350 setup ) ? They should work, all have an integrated RF receiver and they use the same auxiliary dimmer ( MA-R ) provided also by URC lighting dept.
and they are addressable on the same 418 mhz band.

( I called urc - they say you have to buy only the Lutron URC products, I called Lutron - they say it should work )

Actually i found the answer on Lutron web site

Compatibility

Do these Matesro Wireless components work with the existing Maestro Wireless controls or the URC OEM solutions?
No, these components operate on a different frequency and use a different protocol.

What frequency do they operate on?
They operate on 434 MHz.

Do they work with AuroRa®, RadioRA or Homeworks RF?
No, the RF protocols are different. Maestro Wireless components have a one-way protocol, and these other systems have a two-way protocol.


Also i found out about another version of MX-6000 - it's called MX-6000i which works on 434 Mhz ( regular MX-6000 works on 418 mhz ).