I've heard the same about ornamental hops. But they could also be wild hops, which would work for brewing, but would be unpredictable. Heck, they could even be a cross-variety with any number of possible lineages. The first thing I would do is ask your colleague what the origin is. If they're a commercial or wild variety, you're probably okay. If they're ornamental, I wouldn't be discouraged. Maybe you can find some growing somewhere else.
If they're not ornamental, get a hold of the cones and give them a touch/taste/smell test. You could even buy some hops from your LHBS and take them with you for comparison. You're going to want them to have a similar spicy, floral, herbal, etc quality. Some wild hops lack the alpha acids to make them really suitable, but, even if they seem mild, you could try them or even use them in combination with some other variety. Making a mini batch, as flars suggested, to test them is a great idea. You can pitch them in fresh picked. If you're not going to use them right away, you should freeze them.
I actually really want to try brewing with wild hops. A friend of mine is a botanist, and I'm looking forward to trying to find some wild hops to work with this summer. To me, it sounds like you have a great adventure under way. Let me know how it goes.