PS+ has limited support for + features for other accounts on the console.
PlayStation Plus benefits available to other non-subscribing users on your Primary PS4:
Online multiplayer (subject to any parental control settings on sub accounts)
Play downloaded games purchased with PlayStation Plus discount
Play downloaded IGC games
PlayStation Plus benefits not available to other users on your Primary PS4:
Purchasing PlayStation Plus discounted products from PlayStation Store
Online game save storage
Auto patch download
PlayStation Plus exclusive early access to game trial
So yes you can play PS+ games from the US account and play online, you'll miss out on several features like auto-cloud save backups, and you'll also have to log in with the US account with + to download free games (also EU/US PS+ games are occasionally different, especially on PS3). I'd strongly recommend getting PS+ on your main account rather than fussing with multiple accounts. The save data backup is nice, and the discounted games can make up for part (or all, if you buy a lot) of the subscription cost quite easily, as games are often an extra 25% or so off during sales with PS+.
Acutally you can; my brother is doing it with a friend, but it's tricky. It's like buying plus, having your account on both devices and interchanging devices with someone else.
Take: Skynet (my brother's PS4), and Cerebro (his friend's); Charlie (my brother's account) and David (his friend's).
There's an option in the PS4 that says something like: "Activate Device" for "Game" and for "Video", to activate a main account on the device.
David has Plus privileges on his account but his 'Active Device' is Skynet, and vice- versa Charlie has Cerebro as his main device. And they both have their accounts on both devices (main and secondary).
So on Cerebro are both accounts, Charlie and David. Charlie is the main account of that device but it's on David's house; and on Skynet too are both accounts, David is the main account, and it's in Charlie's house.
Basically David+ is playing with his account on Charlie's device, in his own house (as if he were a guest in his own device), and Charlie is playing in his house, with his account on David+'s, device.
Cerebro (in David+'s house): Skynet (in Charlie's house):
> -Charlie (Main) -David+ (Main)
> -David+ (2nd) -Charlie (2nd)
This way David+ can play online on Cerebro and on Skynet, because his account has plus, and Charlie can only play online on skynet because the main account of the device has plus and enables all accounts of the device to enjoy the plus privilege of online play.
And yes: anyone of them can buy a game and download/play them on both devices.
Best Answer
Yes as long as the game you have purchased isn't region restricted for play. You probably will not know this until after you buy the game and try to play it from the other account though.
I have both US and JPN accounts on my systems and play the Japanese titles from the US account all the time (and visa-verse).