Although the answer between distinctly different brands is definitely NO!!! it is of course possible to do so with 2.4 GHz R/C that has simply been relabelled. Such as the Hobby King brand, which is also sold as Copter-X, Exceed and I believe Turnigy.
It surely would be nice to be able to use the low priced Planet RX's with the (slightly) better quality Spektrum TX's instead of the grossly overpriced Spektrum RX's.