OK to drain humidifier into basement floor drain
The humidifier should be draining either to the outside - like rainwater, away from your house - or to a real sewer drain. I have a floor drain which actually connects into the main sewer pipe. It sounds like your drain does not, so I would not recommend draining into that hole.

Many people have a similar problem with the condensate drain from their central air conditioner. Those who don't have a drain below the condensate output have to put in a condensate pump to get the condensate to a drain or outside - and failure of those pumps can result in a flood.