It is! I once made some blackberry and plum wine and it was strong, full bodies and sweet. I used 4lb blackberries to 2lb plums and 2lb sugar. It took a year to age and it was one of my best wines ever.
Blackberry wine is something that my husband wants to try to make. Hopefully he will do a good job of it when he gets around to it. I have yet to find a bottled blackberry wine that doesn't taste and smell like rotted fruit.