[Mivereous]

Attempting to use a Hiding Spot in a Desert does nothing, whether you are next to, or on top of, the Spot. Enemies can still spot you, aggro towards you, and attack you. Attempting to use a second time gives the "You've already used it as much as you can." message.

This is probably also the case with Whirlpool Hiding Spots.

[Neus]

Are you sure? Enemies shouldn't be able to see you while you're in a hiding spot unless they've already spotted you (or someone else).