Color me skeptical. Billy goat shoots blanks which is why Webb Hubbell was pressed into service. Still, just to be sure this fellow should demand DNA testing so his claims can be fairly tested. Hilliary would almost surely support this demand as his mother told her Billy goat is the baby daddy and Hilliary knows women never lie about such things.
In theory a Y-chromosome test from FamilyTreeDNA could show if he shares Bill Clinton’s Y chromosome (which should be that of the Blythe family unless Bill Blythe wasn’t Bill Clinton’s real father). Roger would have a different Y chromosome.