Eh. I wouldn't say it's flat-out illegal. Just add something to the effect of "This card can be used with Ra's Disciple for the synchro summon of a "Ra's" synchro monster" and everything would be alright.

You know what would be cool, thinking about it? A set of cards that are all easy to bring out with each others effects with some mild lockdown, but all had the same name. Like the early Harpie ladies, so you'd have to pick and choose what effects you want to keep while you're building any deck with them in it. Make it engine-themed and you'd get a pun out of it, too.