If I recall correctly, SCMS prevents the player from emitting any digital bitstream if the flag bits in the recording have marked it as restricted.
You may be confusing SCMS with the various copy protection schemes that have been used on commercial videotapes and DVDs, which emit a video signal that can be watched on a TV set--but various shenanigans in the vertical interval make it difficult or unprofitable to copy the same signal.
Unfortunately I don't know what's causing the problem you're describing, but I would try playing back the tape on another DAT deck. Despite the elaborate auto-servo-alignment system that's part of the DAT specification, I remember from the early days of this medium that if a tape was recorded on a Panasonic, you had to play it on a Panasonic and not a Sony, and vice versa.
Of course all DAT recordings from back then have deteriorated by now to the point of being marginally playable at best no matter what deck you used--but I would only expect that to intensify the problem of tape incompatibility and the need to play back certain tapes on certain machines.
Again, all this need for concern is completely contrary to the design of the medium, but it's the way things worked out in practice nonetheless. "The best-laid plans of mice and men ..."
--best regards
P.S.: In my experience, full-size DAT decks sometimes play tapes back more reliably than ultra-miniature, portable recorders; many of the portables have half-sized head drums and force the tape to bend around a very narrow radius, while the tape-to-head contact on the larger units seems to be better.