I wouldn't take the risk. Uncooked rice can make a person sick, probaly a rat too. We cook it to get the germs off. I have five rats (I breed them) and they really like salt licks, cheese its, wheat ins, saltine crackers, basically, mostly all rodents like salt, try stuff that is salty, not faty or chewy, but that it can gnaw on. Good Luck!
Yes, pet rat can eat raw and uncooked rice which will not be harmful for its health.
No, atlease boil it or just give him different food such as bread.
I'm on the 'I wouldn't' side as someone who bred and raised rats for many, many years (lol, you should see peoples faces when they find out I have cremated rats). If you are going to give a tiny piece I'd do cooked at least. Also like many serious fanciers I ended up with my own special diet, lol. Base consisted of Lab blocks (now packaged and sold as rodent blocks I think), bird pellets (pretty bird ect.) vegetables and some fruit on occasion. Cheerios are a good snack and occasionally some uncooked pasta with no artificial flavors or coloring. Things like that. After several years (selective breeding as well) my babies averaged a life span of 4 or 5 years with some going until 6. Here is a good site if you haven't come across and bookmarked it yet.