Not in my experience. I've had both ATAC and Crank Bros. pedals and
the cleats would not work with the other brand. Incidentally, I prefer
the ATACs, they are a much more durable pedal in my experience.
Smokey
I have just switched to Time pedals (Alum ATAC on my road bike and Z
ATAC on my mtb) from Crank Brothers (Eggbeaters and Mallets) and I
have not got round to changing my cleats yet.
Crank Brothers cleats seem to work just fine with a very firm and
secure action on both sets of Time ATAC pedals.
I have not tried the proper Time ATAC cleats yet so I can't say if
they are any better or even different.
I have not tried Time ATAC cleats on crank brothers pedals either.
I would say that it is worth a go.