In theory they can be mechanically, in practice high ADAS standards and functionality like regenerative breaking make it feel like a pretty high risk proposal to allow an end user in.
It's no more difficult to make safe than household wiring, and DIYers work on it all the time.
Driver assist has nothing to do with what type of fuel and powerplant a vehicle has, and those features can be broken by DIYers on any vehicle type. Sometimes being able to disable them is a built-in necessity for safety, for example when driving on gravel roads where they tend to do more harm than good.
Modern ADAS is a whole lot more integrated on EVs than it ever was on combustion cars, not by some inherit requirements of EVs but due to consumer demand when considering a new ev platform.
The driver is increasingly more removed, things like drive and break by wire go through a long chain of controllers in order to allow ADAS, and the input from the user is really just one more signal from a sensor.
There is no longer any circumstance where these systems are completely "off". And none were I would consider off to be safer. (Yes, even gravel and snow)