Non MLS Sales - The Shadow Market in Non-Disclosure States

I would like to know what real estate agents, mortgage loan underwriters and appraisers feel the impact of builder/developer-owned closeouts, marketed and sold as pocket listings (non-MLS) have, by artificially inflating values in deteriorating markets, especially in non-disclosure states like Utah.  In my opinion, these non-MLS closeouts DO represent part of the true market (just as short sales and REO properties), and should be incorporated into sales comps that are included as comps by appraisers, but... are may not be.  If buyer's agents are not made aware of these "firesale" programs, the last line of defense is the appraiser, who may not have access to this non-MLS information.