It does kick up some dust. Pun intended.
There are a lot of issues with this card.
If the Permanent is used for both Hiding/Unhiding a creature, then effectively that card has two active abilities. Or one active ability that does two things, depending on if the creature is 'Hidden' or 'Unhidden'. For we will have to create a new status. Or else, you could 'Unburrow' a Shrieker that burrowed itself, and is technically not in the Foxhole.
As Unionruler points out, can we burrow a creature on the turn it is played (I think so), but if we can un-hide a creature, and let it use its ability on that same turn - it could lead to abuse, enabling players to effectively use a creatures skill on the turn it was played by burrowing and then unburrowing it. This will amount to more code and more testing.
And, as mentioned before, what happens if the Foxhole dies? Sure, you mention the creatures get unhidden and take 1 damage? But I think more importantly, what if the Foxhole (permanent) is stolen? I think for arguments sake it should be immune to steal, but still be able to be destroyed. But then again that is a new status. Or maybe an attempt to steal it destroys it? But then the card itself just becomes quite complex.
Your thoughts?