An Oracle's Curse counts non-Oracle levels as 1/2 for bonuses.
A "typical" Oradin has a fair number of Paladin levels, probably more Paladin levels then Oracle levels.
Random-ish examples:
An Oracle 2/Paladin 6 would count as 5th level for Curse bonuses (2 + 6/2 = 5), and thus Haunted would (try to) grant you Levitate and Minor Image as Oracle Spells Known. But a 2nd level Oracle does not have any 2nd level spell slots.
Likewise an Oracle 6/Paladin 8 would count as 10th level for Curse bonuses (6 + 8/2 = 10), and thus Haunted would (try to) grant you Telekinesis as an Oracle Spell Known. But a 6th level Oracle does not have any 5th level spell slots.
It will at least add the spell to your Spell List, for things like UMD-ing wands and the like, so it isn't a total loss, but not really ideal either.
I will go edit for improved clarity.
Go for it.
Unlike most 3rd party DSP has a solid enough reputation for throwing stuff in the guide.
But I warn you, I'm not likely to read up on it too much and will likely just copy/paste anything you post straight into the guide
On a related note: any good Path of War stuff that would help?