hearing aids work with compression. Also, they don´t fully restore your hearing to 0 dB loss.
If you have, for instance, 60 dB hearing loss at 3 kHz, then for soft input (50 dB), you get maybe 30 dB amplification, for 65 input 20 dB amplification, for 80 dB only 5 dB amplification. Then you have the mpo (maximum power output), which is an absolute barrier. This is often set to values between 90 and 100 dB, so you won´t ever get a sound louder than the mpo at that frequency from your aid.
Problems might arise when:
- you have severe hearing loss, then you need high amplification to understand speech, thus you might in fact hurt your residual hearing
- the aids are not set up correctly
- you are exposed to loud sounds for a long time
I mean the following with the last point: If you are exposed to levels about 60 - 70 dB the whole day, then the aid does in fact even increase this level. Thus, the total dose of noise is increased, which might - even if it´s not extremely loud - hurt your hearing over time.
As a musician you will already have guessed by now that all this compression is noticeable.
But generally, modern hearing aids are quite safe to use.