Its comes down to everything being on the same frequencies, the iPhone hotspot only uses 2.4ghz, depending on your operator LTE uses 2.1ghz, 2.6hhz,1.9ghz, 1.8ghz, all of this COULD cause problems, the best way would be to have a 5ghz wireless hotspot and do it that way, some people are reporting issues with wifi turn on their tablet some are not,
Personally I'm working on the side of caution, i have always avoided all forms of possible interference, the only upside it IF it did cause a problem its on the RC side and the craft should enter failsafe.