Yes, atmospheric pressure will be higher, which helps somewhat with NPSH (available). Just as the air gets skinnier when you go up, the air gets fatter when you go to depth.
Ambient temperatures in an underground mine are dependent on a host of variables, including but not limited to: virgin rock temperature (VRT), airflows through the workings, age of the mine openings, air temperature on surface, "wetness" of the mine, cooling/refrigeration plant capacity (if used), diesel engine and electrical loads, production rates (tonnes mined per day), etc. Having said all that, I've been in plenty of mines at depths of 5000 feet (and deeper) and while it is warm, most mines are not unduly "hot". Most mining jurisdictions & mining companies maintain temperatures below about 26 Celsius (wet bulb); 80 Fahrenheit. Don't forget that people have to work in these environments.
Cheers,
CanuckMiner