I am not able to find Cato Hostilius........the map keeps sending me to Vault 34 but no Cato. What am I missing?

Are you sure you have the right quest activated in your pipboy? According to the wiki, Cato is located between Ranger Station Delta and Hoover Dam.
If you have activated the Arizona Killer quest, you should be able to find him by following your map marker.

This happens all the time. You need to remember to activate the right quest in your pipboy.

Thank you!

Going by the name, I'd bet it's one of those Caesar grunts, and as such, they explode in my sights, quite nicely, thank you.