My brewer's best German Oktoberfest kit came with 1oz of Vanguard hops as a finishing hop. It was supposed to come with Hallertauer hops, but they substituted Vanguard instead. In Papazian's complete joy of home brewing book, the table of hops lists Vanguard as "Good all-around hop similar to U.S. Hallertauer." I actually just cracked open the first brew after 2.5 weeks in the bottle and it was quite delicious, well-balanced. I certainly didn't notice anything offensive in terms of hop flavor or aroma. I'd say go for it, but then again, I'm still somewhat new to this and don't know a whole lot about hops yet, so take it for what it's worth.
I brewed a hefeweizen with 1oz vanguard 3 weeks ago. They've only been bottled for 2 days though so I haven't tried any yet. My LHBS also recommended vanguard since they didn't have any hallertau. I think the vanguard will be fine since I wasn't really looking for a lot of noticeable hops just some background bittering for balance.