Yes, the wedding is presumably still valid... if it was actually consummated (i.e. Edmure and Roslin had sex).
As far as I can recall (and the Wiki of Ice and Fire backs me up), marriage in Westeros generally requires the two participants to willingly exchange vows, and then consummate the marriage in bed.
A wedding that has not been consummated can be annulled. I believe this came up with the marriage of Tyrion to Sansa, since he did not force her to consummate it.
However, failure to consummate doesn't mean they aren't married, just that it can be dissolved.
They clearly were brought up for the bedding ceremony, although I don't recall if there was any indication of what happened after they were stripped and thrown in the bedroom. I recall that Roslin was distraught:
Poor Roslin's smile had a fixed quality to it, as if someone had sewn it onto her face.
'To bed! To bed! *To bed with them!' Roslin had gone white. Catelyn wondered whether it was the prospect of losing her maidenhead that frightened the girl, or the bedding itself.... Catelyn felt sorry for the girl. Most brides tried to return the banter, or at least pretended to enjoy it, but Roslin was stiff with terror, clutching the Greatjon as if she feared he might drop her. She's crying too, Catelyn realized..."
But fear of her grandfather would likely keep her from revealing anything to Edmure, and he certainly seemed willing, and unaware. So it seems likely the marriage was consummated.
The vows were certainly exchanged, and exchanged willingly, so the circumstances of the later wedding... "activities"... do not change the status of the marriage. Only Edmure's opinion of his new family.