Not sure, but its a pretty sturdy building. They have their own diesel generators for power as well.
I would try calling or emailing them. The GM there is:
MANFRED PIEPER
General Manager
Hilton Guam Resort & Spa
P.O. Box 11199
Tamuning, Guam 96931
646-1835 Fax: 649-1190
[email protected]