I used ethanol for PFA fixation and paraffin embedding. It worked in regular ISH (BM purple substrate based). However, I am not sure it will work for fluorescent in situ hybridization (FISH) if that is your goal.
Yes, definitely. I use EtOH routinely on whole mount ISH, its works very well. You might need to adjust slightly the permeabilisation step (slight increase) depedning on your tissue.
I do not manage to make RNAscope in situ technics work with EtOH dehydration though so I still use MeOH for that.