Not a problem... just remember to make that poison save as you are directly putting it on YOURSELF. And a saving throw each round of exposure until you've passed the poison to an intended target. The whole thing about poison use as a class ability is that it allows you not to accidentally do to yourself what you'd be doing DELIBERATELY. Effectively you're circumventing the poison use ability by trying to apply poison to your natural weapons.
well poison use should by wording allow it for injury poisons at least.
Contact is kinda iffy.. you don't poison when applying but then.. your onstatnly touching it so it would go off on you...
There are also specific feats for applying it to fleshy bits (adder strike and a few racial specific feats) that deal with poisoning natural..
Interstingly you could in theory use poison use and mouth to store inahle and blow it on someone
Note- the alchemist, which is a fairly popular class for natural attack builds due to a discovery that grants bite/claw/claw, eventually gains poison immunity at level 10 via poison resistance (which also gives bonuses to saves against poisons prior to that)
Druids also gain poison immunity (referred to as venom immunity) at level 9. And I do not need to go into how well they work with natural attack builds, right?
So there are always options.