Also, the ham bands as a whole cannot be used for profit-motives or any financial gain. People often forget this rule. Not to mention the (kind of absurd, IMO) rule against any form of encryption.
almost every single repeater I know of uses this method for remote control. I even remember listening to someone sending long strings of high speed DTMF, presumably to try and brute force control of the repeater. One of the managers said they weren't successful
In the US, there certainly is. The rule doesn't mention encryption specifically, it just prohibits "encoding for the purpose of obscuring meaning". The intent is what matters not the method.
Repeaters may use any method to limit access and control to authorized users.