Yes, that's a quite common design. It might be forbidden if you expose that outside the device, but in electronics internal to the device you can do that no problem.
Unless I'm missing something I don't think so. The case has mains voltage in and switched mains voltage out only, to touch the low-voltage bits with the weird ground level you have to crack open the case. Which is kind of encouraged by open design that's easily hackable, but something that falls under "well, if you do that you're supposed to know what you are doing".