Are hotels and restaurants, including star-rated hotels, allowed to let anyone or strangers in and out at will?

I don't know what you mean. If you mean the public places of hotels and restaurants, in that case, if you don't dress like a beggar, you can go in and out casually as long as you dress neatly, but only employees can go in and out of hotels and restaurants, and non-employees and non-staff people can't go in and out. For example, the staff passage usually warns that non-staff people are not allowed to go in and out at will.