I think a distinction might be drawn between using a GPS device to stay safe and using one to get an advantage over race rivals to win prizes/medals.
As to rules: rules follow abuses and cases eg EPO wasn't illegal in cycling until riders started using it to advantage and then a rule had to be introduced and in fell running until Ted Pepper died in the 1978 3Peaks race there were no FRA safety rules but for the last 40 years there have been.