I have not doubt that foreign agencies are still spying on Trump (and Obama, Bush, Clinton, etc.) I would guess they would be more likely paying folks already on MAL payroll, rather than trying to create a cover that certainly the SS is thoroughly vetting. That's a pretty valuable asset to risk on an ex-President. So, probably no trained spies working as bellhops. I would also imagine there have been trained spies who have been invited by guests and/or Trump himself.
There may be US intel there as well, but the political implications of the CIA spying on Trump would be huge. If they are there, it's probably more counter espionage to any of the folks from other governments. I doubt that they are going into any of his private rooms or eaves dropping. I hate Trump, but I would be pissed if the CIA was freelancing like that. And if they were, they wouldn't be sharing broadly across the agencies.
All just guesses.