I actually thaw frozen rodents in cold water, & change the water (depending on how big they are & how long it takes), so that tends to wash off such contamination
& some of the scent, but that said, I've never seen snake that objected to rodent droppings, & they even eat them backwards sometimes...
Now spoilage is another thing altogether...if that's the case, that can make your snake ill, & there's no excuse for that, unless you thawed them incorrectly.
Thaw in refrigerator, which takes a LONG time, or thaw in COLD water, which is much faster; never thaw rodents by leaving them setting out at room temp.-
& if you thaw rodents in WARM water, they can spoil on the outside (where they thaw faster) before the insides are completely thawed. Remember that
frozen foods aren't bacteria-free...it's there but dormant in freezing temperatures, & when you thaw it, bacteria comes to life & causes spoilage.
At some point, we can smell if rodents are spoiled...but snakes have FAR better noses than we do & will know things that we don't.