I've not seen anything about Diovan that suggests it can cause hair loss, though if you're worried, you should certainly talk to your doctor.
There are also plenty of good meds available that help with hair loss, so your doc should have some help either way.
Here's the official site so you can read about your medication:
http://www.diovan.com/index.jsp?source=01030&campaign=CVZ-9473&site=100005&placement=105426&creative=100002&usertrack.filter_applied=true&NovaId=7852773720739533443