Who bot should recognize <first name> <last name> and not just <last name>, <first name>
In my org, Who bot only recognizes names if they're listed as <last name>, <first name>. There are specific, limited instances where it will recognize a user by <first name> <last name>, but for most users this simply gives an error message.
Interesting, this isn't the case in my org, as first-name-only queries work; so it may have something to do with how your org stores data.
That said in either case, WhoBot should be able to handle this case properly.