Sorry it took us so long to respond.  In a word, "no" the offer can not be accepted.  Yes, the DFARS and AFARS lacks any further latitude because the FAR is prescriptive with the use of "Shall" at 4.1103(a)(1) and with "are required to be registered in SAM at the time..." at 4.1102(a)(1).

If this is a concern, and none of the exceptions 4.1102(a) (or at 4.1103(b)) will apply, your solicitiation should highlight the importance of SAM registration to all potential offerors.