not rly, the story show they are evil and completely against the living, the faction would not want then in their ranks, and they would not want join their ranks to be servants, when they being power hungry would want to lead. Forsaken had an alliance of convenience with a common enemy of the alliance, What the san'layn have to offer or to ask for the horde? Forsaken broke free of the Lich king and most of then were not just evil spawns of him who keep doing evil deeds, unlike Sanl'ayn that we don't have a single exception of not doing evil shit
There is also no population of then, they were supposed to be extinct, and a race who only exist by killing more elves and putting then a worse curse than the DK curse is kinda fucked up, what makes Venthyr a better suited race, since apparently they are their own race
but my main point is: 1)there is better options of a vampire race, 2) if is san'layn they would need way more time to build that shit up(and i doubt it would even be good, but that is just me) not just on the fly, 3) there is other races better suited who should come first. and 4) we have plenty of elves for a while, all this nonsense with HE should give us a break about elves