Vernon is one of those names that is so dated and stereotyped that it would be kind of a statement to use it. Like, if your family tends to be goodlooking and talented with a great sense of humor, you could totally use it. It says "I'm so cool, I make the name
Vernon cool."
I grew up with a kid named
Vernon, a good friend's little brother, who was
Vernon Middlename Surname IV. He was a fun person. And nobody called him
Vern. His middle name (a surname name, I think) started with V and ended with N, too, and it sounded cool.
Vernon Theodore sounds fine. If I liked
Vernon I'd be tempted to use
Vernon Victor or
Vernon Vincent.