Are Hitec servo plugs compatible with futaba?

You betcha!

Yes but.... The male Futabas have a small tab on the side which must be trimmed off in order to plug them into a Hitec receiver or connector. Other than that, no problem.
Dennis-

But he's taling about HiTec to Futaba....

I realized that, but if he's going to have both Hitec and Futaba equipment, he's eventually going to try Futaba to Hitec.

Just thought it would be worth mentioning (in case you weren't aware) Hitec servos are available with Futaba "J" connectors.

Its a good thing they are compatible. I put in my hitec servo's into the wings of the plane im building then I realized i was using futaba electronics! Good thing i dont have to go throgh all that again

Yeah.

My Hitec HS-327HD has a Futaba J connector and (to my surprise) actually has a faster speed than my S3004's.

Whoa whoa whoa.. What do muffins have to do with explosions???