Es correcto usar las dos, como hablante español no encuentro alguna equivocación Saludos!!

"LE" is the way to shorten "A quien sea/ a alguien...", so I would say: "Pregúntale" or "Pregunta a quien sea", but not "preguntale a quien sea" It is not a great mistake and anybody will understand it, I think that many spanish will say "preguntale a quien sea", but it is not so correct