Notice that the cited article is from New Zealand where this usage is apparently common. There, to "trespass" someone is to serve them a notice that you want them to leave your property ... if they remain, or return, then they will have committed criminal trespass (https://www.police.govt.nz/advice-services/personal-and-community-safety/trespass-notices).
Note that this usage is similar to saying that someone has been banned or "86ed"--meaning (following Wikipedia or MW) to refuse to serve, to get rid of, or to throw out.
So the headline 'Criminal trespasses police officers' could be read as
Criminal bans police officers
and
The entire police force has in effect been banned from a Wellington property.
As for your final question, whether it's "legitimate" depends on whether you're a descriptivist or a prescriptivist, and if the latter, what your standard is. One could argue either that the lack of entries in dictionaries makes it illegitimate, or that repeated occurrences of this usage, found via web search, makes this a new usage that will eventually be stamped with legitimacy by lexicographers adding it to dictionaries.