Yes, it is okay to put in $0 for your second employer as MA wages as long as both states have the exact same amount in Box 16. The wages should be sourced to RI since that is where the work was done, assuming you were not a telecommuter and you worked in RI. MA will still tax it as your resident state and give you a credit for the tax already paid to RI, but if you have the wages sourced to both states, you will be double-counting the income for MA as you said.
