Legally, it would need to be cleared vis a vis emoluments, I'd expect. Politically, it could be seen as a bit tacky, unless the other leaders agree that it's an appropriate venue. He's obviously showing off here, and no doubt, hosting the event there shows some bravado on his part. Going forward the resort will be able to claim it hosted the G7, which might raise its profile.
If it's cleared legally, and the other leaders agree with the arrangement, maybe it works. George W. Bush used to host world leaders at his ranch in Texas. I wouldn't otherwise have a strong opinion, though it's pretty much expecting everyone to go along with Trump's schtick as being somewhat of a show-off.