Can you create duplicate character names in Planetside 2?
No.
Every single character of any user of any faction on any server has a unique name.
Although first-hand evidence is hard to come by in the form of a FAQ topic or something similar, there are enough leads:
-
It can be inferred from randomly found screenshots of character screens;
Or from visiting fora threads like this one.
This has probably played a major role in how in Planetside 2 "every username is already taken".
Advice: change the capitalization of one of the characters, since it will register as a unique username (unless taken, of course).