Even if the hotelier could find out, he would be sued, and most likely sued into bankruptcy.
What is being implied is that all believing Christians need to get out of any business that could potentially support an invalid marriage. This would include: restaurants, hotels, motels, B&B's, banquet rooms, bakeries, flower shops, stores that have wedding registries, wedding dress providers, tux shops, caterers, limo drivers, travel agents, resorts, airline companies, bus operators, car rental agencies, etc.
Basically Christians would have to completely extricate themselves from the wedding industry leaving it entirely up to secular folks. Either that or be in constant threat of inadvertently providing support to an invalid wedding/honeymoon or being sued for not providing support for an invalid wedding/honeymoon.
The US used to be a Christian nation. It was quite easy to engage in pretty much any reasonable business without violating one's conscience or religious beliefs.
It now appears that due to recent Supreme Court rulings that there are fewer and fewer businesses that Christians can own or be employed by without threatening their salvation.
Even being a pharmacist is problematic if you are forced to ring up morning after pills.
This is not as simple a question as you make it out to be.
It is, if one is a good Catholic. I'm sorry you don't understand.