As others have said, the only time a conference organizer may care is if their room block is filled, the hotel is sold out and they're turning away conference attendees. That said, in other situations conference organizers would probably be happy because:
1. Some conference organizers take a commission on rooms booked in their block.
2. Some conference organizers negotiate extras based on the number of rooms booked. (The organizer may get free hotel rooms, upgrades, etc.)
3. Hotels look at an event's historic room pick-up when booking future events and negotiating contracts. The higher the room pick up, the better it is for the event organizer.

As an event organizer, I would always give the hotel a list of my conference attendees to ensure we got credit for people who might have booked outside the block. (We wouldn't force them to rebook at our rate, but the hotels usually gave us credit for these rooms which wouldn't have otherwise been booked.) There are often conference attendees who aren't officially registered but are booked into a room block, so I can't imagine the hotel taking action to remove someone from the room block if they weren't on the attendee list. (For example, some of my bigger exhibitors might have exhibit designers/managers who were only on the show floor for setup/teardown, or other staff who were doing demos in suites but never attended the actual event.)