Like so many things in life the answer is "it depends"
We actually had a hearing impaired young lady in our 4wd group for a while and radio comm was her big challenge (we were working on mobile wifi and laptop when she sold her rig)...she overcame this by having a passenger run the radio that she could sign to...
In a hiking situation...
with a group the concern would be trail info and alerts....but hand gestures (stop quick -snake/bear/big cat) and facing the person for lip reading would help...
Solo the trouble is wildlife (rattles, snarls, roars and such), rockslides, oncoming vehicles like bikes, atv's and such and those things we take for granted....
Lastly I ask if this is for you, someone you know or just a general question....and do you need more info as I would be willing to research more and contact hearing impaired resource groups if needed.
thanks