i want to make it clear that yazid was not a sahabi… majority of historain say that he was born 25 hijra.
RA means here rehmatullah alle, that we use for tabian and other muslims. he was a pious and learned person as imam bukhari and imam muslim had not mentioned nething negative about him. historain has mentioned mixed opinion him. since majority of tabian and sahaba did bayaat of him i think there is no point we should not place rehmatullah alle after his name.