compensation

If a plan uses 3401(a) for the def of comp, then that excludes group term life correct?  The plan does not use w-2 def of comp, which would include it under 6052.  They also do not exclude fringe.

I take it you mean the value of the premium used to pay for coverage in excess of a $50,000 death benefit? (The cost on first $50,000 is simply excluded for income under Section 79.)

Yes, the excess premium amount would not be counted if you are using 3401(a) because that excess premium amount, which is of course included in box 1, is not subject to withholding and 3401(a) defines wages subject to withholding.