They do check magic bands
From DVC member site:
Top of the World Lounge Access
Top of the World Lounge is located at Bay Lake Tower at Disney's Contemporary Resort. Disney Vacation
Club Members staying at any Disney-owned-and-operated hotel at Walt Disney World Resort (
whether they booked with vacation points or cash) may enjoy access to one of the vacation kingdom's most exclusive spaces: Top of the World Lounge atop Bay Lake Tower at Disney's Contemporary Resort through December 29, 2015 (blockout dates apply. Including but not limited to 12/30/14, 12/31/14, 7/3/15, and 7/4/15). Current operating hours are 6 p.m. to midnight.
This perk is available exclusively to Members and those in their traveling party who are staying on that Member's reservation.
At least one Member in the traveling party must accompany the group and present his or her current Magic Band or Key to the World card with a Disney Vacation Club Membership notation in order to gain admission to the lounge and observation deck. If the Member's Magic Band or Key to the World card doesn't display a Membership notation, a Disney Vacation Club Membership Card is required in addition to the Key to the World card to verify Membership.
Note that Members traveling from other Resorts must use Walt Disney World Transportation, as
parking is unavailable to anyone not staying at Bay Lake Tower or Disney's Contemporary Resort. Upon arrival, Members must walk to the Bay Lake Tower main lobby entrance on the ground floor and check in at the Top of the World Lounge desk in the lobby.
This special Top of the World Lounge access is available on a first-come, first-served basis until the lounge reaches capacity. As the lounge is particularly popular during the Magic Kingdom fireworks, arriving as early as possible will give Members the best chance of gaining admission.