I'm afraid the answer comes down to "ask your employer."
My company is in the computer industry and old enough that we date back to eight-character user names. That has innoculated us against expecting user names to map directly to actual names; there just wasn't enough space to do anything but a contraction or alias. That also means we have mechanisms in place to ask "who is this actually" -- user profiles that can be searched by userID. Those mechanisms have persisted, and these days most users have both a my-name@my-site address and a shorthand [email protected]
In our environment, I agree that if your shortname looks like someone else's name -- unless completely obvious as a fictional reference, and maybe even then -- it may be needlessly confusing and will be discouraged. And of course anything offensive, rude, annoying, or otherwise immature and inherently unprofessional (l33t is right out) will be rejected. But as long as you aren't gratuitously stupid about it, everyone recognizes this as just a nickname and nobody much cares. I am probably more widely known by my username than by my actual name.
But your employer may not be this flexible. Some do have stricter policies. Ask them, not us!