Can you , yes. Harboring a fugitive is a felony. In other words, knowingly aiding a wanted person is a crime. It is not typical, though, to be prosecuted for that offense, at least in my experience. It can be a tough crime to prove. However, if this person is wanted for a serious crime, your certainly at a higher risk of getting arrested/charged.
If you want to help this person, he/she should be advised to deal with the warrant. Its not going to go away. Seek the advise of a criminal attorney who practices in the jurisdiction that issued the warrant.
Yes, and depending upon what he is wanted for, don't be surprised if you are charged should the police discover that you have been knowingly harboring him/her.