Are MDD CPU cards compatible with other g4 PMACS?

Reason I ask is i found one very cheap, and I also found a few cheap quicksilver and graphite Powermacs? It is the 1.25 ghz dual cpu version.

No, the MDD cards will only work in an MDD. Different Bus and other things.
Sorry.

in that case, what powermac g4 models have interchangeable cpu cards?

The Upgrade CPU's out there are interchangeable with the Sawtooth, Digital Audio and Quicksilver. Not sure on the factory CPU's but I know people have gotten some CPU's from a Quicksilver to work in a DA for example.

Further Sawtooth and Gigabit Ethernet are both 100MHz system bus speed, and CPU's are interchangeable, Digital Audio onwards to Quicksilver 933MHz are 133MHz bus and SOME are interchangeable, and with MDD there are various bus speeds over the different models so CPU's of the same speed are interchangeable.