I had a sitiation similar to this. My MIL-Mary Dean-passed away 2 months after my husband and I were married. About 6 months later we found out we were pregnant. We decided if it was a girl, we would name her Mary..... Well my SIL is Mary Cassandra(called Casey) and said she gets first dibs on the name Mary since it was hers and her Mothers. We had a boy and named him Michael(hubbys name) Dean(MIL middle name). Then she was pregnant with a boy, then us with a girl. We still couldnt use the name, it was hers. 12 years later she has 2 boys and 2 girls(neither with first or middle named Mary), and we have 2 boys and 1 girl and we win :) because we used her middle name. She was always called Dean growing up anyways(I guess its a southern thing).
If you really like the name and it fits, use it. Im the only J. in my large extended family(both parents are 1 of 9 kids) but there were about 12 in my graduating class, and easily 30 in my school. Someone somewhere is bound to have the same first name eventually.
Use this to see how many there are.