Sharon, I read the Overview for Emma de Conteville as being clear about whose opinion it is.
From FMG, there is a "manuscript relating to St Werburgh´s Chester" that says “Hugo Lupus filius ducis Britanniæ et nepos Gulielmi magni ex sorore” transformed the foundation into a monastery.
Translation: Hugh Lupus, son of the duke of Brittany and nepos of William the Great (William the Conqueror) through his sister" ...
The word nepos is famously ambiguous. Strictly it means a grandson but it was often used to mean nephew. Hugh Lupus was a son of Emma, so she must be the sister and nepos must mean nephew in this case.
But we know from Orderic Vitalis that Hugh Lupus was a son of Richard le Goz. Richard le Goz was not duke of Brittany, and there is no other evidence that Hugh Lupus' father was a duke of Brittany.
So, by digging just a bit we can reconstruct the logic. If the St Werburgh manuscript is inflating Hugh Lupus' ancestry on his father's side, then it is probably also inflating his ancestry on his mother's side.
I wish we had the date of the St Werburgh manuscript. Early or late? But it doesn't seem necessary in this case. The manuscript is problematic no matter what the date.
Just as an aside, I checked Catholic Encyclopedia. It says "in 1093, Hugh Lupus, Earl of Chester, richly endowed the abbey and its church. By the instrumentality of this noble, Chester, which had been in the hands of secular canons, became a great Benedictine abbey"
http://www.newadvent.org/cathen/15588b.htm
That doesn't help much, although it does tell us the St Werburgh manuscript must be after 1093.