It will actually be helpful if you are having any nausea from the hydrocodone . . . the actual level of CNS depression that cannabis causes is insignificant and there are stimulant elements in the mix as well so it is actually in the neutral zone on the stimulation-depression continuum and therefore does not have anything that will really add to or synergise with the hydrocodone in that respect.
The mental slowing and so on from cannabis is from the euphoriant effect, not tranquilliser-type anxiolysis . . . That is also the respect in which it may help the hydrocodone as a pain reliever. But cannabis is not a centrally-acting pain reliever by itself -- it only has ingredients which can mix with a lot of others: for example, a bong hit will help paracetamol, aspirin or naproxen with a headache strained muscle., and even Ben-Gay and so on.