It all depends exactly what the engineer is SSHing into. A bash shell with root access? BAD. A shell with only monitoring and diagnostic tools that are cleared to use while the car is running? Probably not a problem and actually sounds both useful and the right way to do it. I'd love to be able to SSH into my car and get diagnostics.
To be clear, neither is acceptable but it being secure is still a big issue.
The thing with cars is that malicious actors usually can get physical access to it, which makes it an order of magnitude more difficult to secure. This is one of the main reasons car computers often seem so clunky.
Besides, would you dare driving next to the guy that just installed random rom from xda?
The rom on the car is way less of a concern to me than whatever the person had to drink or their road rage fueled tailgating...