Other measures are possible, if there are night porters a register of special needs can be held at reception and a roving staff member sent to assist the guests. Not ideal but standard solution at many hotels. This duty can be also delegated to the team leaders of conventions. A couple of deafgards will probably also be an adequate solution for that size of hotel.
Visual alarms will not arouse a sleeping person but are useful during the waking hours, though how many is it reasonable to fit? The hotel remains compliant with L2 using heat detectors, provided disabled rooms have smoke detectors. Optical smoke detectors will give earlier warning but whether they will help save a person in the room is a moot point and a very old chestnut. The detectors in rooms adjacent to escape routes are intended to protect the escape route and not the occupant of the room. The standard recommeds that disabled persons may need assistance or be siower to respond, so the standard and ADB both recommend DS in disabled rooms. But personally I usually recommend a phased upgrade to smoke detectors as it has got to benefit the relevant person asleep in bed.