Pass without trace says:
A veil of shadows and silence radiates from you, masking you and your companions from detection. For the duration, each creature you choose within 30 feet of you (including you) has a +10 bonus to Dexterity (Stealth) checks and can’t be tracked except by magical means. A creature that receives this bonus leaves behind no tracks or other traces of its passage.
And one of the Cranium Rat's abilities says:
Telepathic Shroud. The cranium rat is immune to any effect that would sense its emotions or read its thoughts, as well as to all divination spells.
With both of these, does this effectively make a druid that is wild-shaped into a cranium rat untraceable (barring undeniable direct line of sight) until one or the other runs out?