Vented gas logs will be composed of either ceramic fiber or solid refractory ceramics. In the case of ceramic fiber logs, they are porous and may need to dry prior to use. With solid refractory ceramic logs, they can simply be wiped down and will not hold water. There would be very little risk in either case as water vapor is already a harmless byproduct of construction and masonry chimneys are not all water-tight to begin with.