If nobody knew he was a male prostitute and he came and went day after day without incident, I would have no problem imagining this at all. Those who are trusted are not tracked like terrorists, period. (And by "trusted", I mean trusted not to cause trouble or danger for anyone inside the White House.)
My question: why didn't the secret service advise the white house (post 9/11) that gannon was unsuitable for private WH vistits let alone white house press corp.
This has been answered time and time again: Because he only got day passes. Those seeking day passes to the briefing room get only a rudimentary security check (have you ever killed anyone, been committed to a mental institution or otherwise shown yourself to be a dangerous nutcase, etc). Gannon/Guckert was and is perfectly suitable for WH visits unless the only thing constituting "suitability" is "Could the Democrats make hay out of him being there?" (And once it was discovered they could, the WH stopped letting him in.)
BTW, I guarantee you that there are others given daily access to the White House - including those who have passed the far more stringent security checks required for permanent passes - who lead private lives that are just as embarrassing as Gannon's, if not more so. They just haven't been caught, and 99% of them never will be. Such is the case in any organization comprised of thousands of employees and daily visitors, and was the case in the Clinton White House, the Bush 41 White House, Reagan, Carter, Ford, Nixon, Johnson, and as far back as you want to go.
Like who?