Does my wife's boyfriend have the legal right to spank my child and "whip" him with his belt?

Absolutely!  You should notify the police immediately if you believe your child is being physically abused by ANYONE...  The Police should conduct an investigation and will probably have DCFS involved.  If the alleged abuse is confirmed, your Wife's boyfriend may be arrested for multiple offenses.   For more information on Domestic Battery, visit my website at: http://davidleelegal.com/ David Lee