If it were me, I'd make sure I knew where the vent is in relation to that drain. If it was originally intended to be a backup floor drain or something, the closest vent might be far away, but regardless of the history, it won't flush well and will make funny noises if it doesn't have enough venting. I bought a cheap 50' usb camera before I did some basement drain work at my house, and ziptied it to a snake and took a look around. I found one drain that I think my kitchen previously drained to that was basically impassible and filled with sand and rock below the slab, for example, so sometimes when you find a drain that's mysteriously not in use, there's a reason.