Not some spells. Geeze it's really easy. A unit with Resistant Skin is considered a Hero unit for spell targetting - thus all fields that are related to Hero units will be applied to non-Hero unit with Resistant Skin as well.
Duration - Normal -> applies to normal units (that don't have Resistant skin)
Duration - Hero -> applies to Hero units and units with Resistant skin.
Same logic applies also to "Targets allowed" table.
If that field has "Non-Hero" checked, then you won't be able to target unit with Resistant Skin, since this unit is considered hero unit for spell targeting, thus it won't return true for the condition that the target is "Non-Hero".
Because Devour, Finger of Death and Charm have all "Non-Hero" checked in Targets Allowed table, you will not be able to use it on Non-Hero unit with Resistant skin.
Other spells that you won't be able to use on unit with Resistant Skin are e.g. Transmute and Doom. Just follow the logic of the 2 facts above and you will easily understand how Resistant Skin works.
Or if you have trouble with that, then just ask yourself: How does *some spell* work on heroes?
That question will answer you how it will work on units with Resistant Skin.