The genotype of all Douglas' hairless rats would be the same as far as the hairless gene is concerned. It wouldn't mater if they came from het X het, or het X homozygous, or homozygous X homozygous - all the hairless ones are homozygous hairless. If the hairless rats from out-breeding projects are better it's because of other genes they either got rid of or picked up through the out-breeding - not the hairless gene.



Now if the hairless gene does have some secondary ill effect then it could get a little more complicated. While you would expect to see the problems in all hairless rats regardless of their pedigree you might eventually accidentally pick up a separate gene to compensate in out-breeding. But if you are consistently seeing better results with out-breeding then the problems in the original colony where almost certainly due to more than just the hairless gene.



I did read about hairless Syrian hamster female's not being able to nurse their young as an apparent side effect of the hairless gene it's self. For this reason they use only het females and probably do a fair amount of incidental out-breeding but I don't know if they still see other problems associated with the hamster version of the hairless gene or not.



I did find an interesting (but old) article today about a scaleless snake being found not to cool/heat convectively or dehydrate quicker than a normal one. Maybe the scales are primarily to protect against rough environments or (since their bodies are down in them) or even ants or biting flies or something in the wild.



It’s also interesting to see the variations in scaleless snakes and to note that none of them have become common place yet. It may be like albino in that a number of different things can go wrong producing slightly different scaleless versions. Maybe some of these have had problems that have held them back from becoming popular in the pet trade.
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