Hi Scott,
I would recommend moisture bake-out prior to LF-soldering for all PCBs, since 
the vapor pressure in the PCBs is double than what it would be for 
SnPb-soldering.
You also say: "My understanding baking boards also have risk and can cause 
the intermetallic layer to increase with ENIG boards.  I've read this in several 
white papers and in seminars I've attended."
The IMC layer growth concern is a 'red herring' that every so often gets 
mentioned as an aside or by people who do not know what they are taking about. 
That has been the case with soldering to Cu where the Cu dissolution rate is 
50-times faster than is Ni—IMC layer thickness for ENIG is not a concern you need 
to have.

Werner



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