It ought to work, but some people will say the concentrate is of grapes grown for wine and the juice is of grapes grown for eating/drinking, and they're different - eg in tannin levels.
OB is bang on. They are not made from the same grapes. What are you trying to make? you could use som WGJ and sultanas and you might get close to the same effect as the concentrate.
It was more as a check before I thought about doing anything really, probably looking to do a sherry, some of the recipes I have call for white grape conc, others don't. The recipe that made me ask already has 1lb of raisins anyway.
