Not all all Garmin devices are "custom map capable" an attribute that permits a user to load KMZ files – often a desirable feature.
Unfortunately it’s not as easy as you might expect to access a list of Garmin map capable devices. 
Garmin appears to moved away from an all in one list to some classification system. 
However the following list of handheld devices could be a good starting point for disaster recovery application.

Colorado series (300, 400c, 400i, 400t)
Dakota 10, Dakota 20
eTrex 20, eTrex 30
eTrex 20x, eTrex 30x
eTrex 22x, eTrex 32x
eTrex Touch 25, eTrex Touch 35, eTrex Touch 35t
GPSMAP 276Cx
GPSMAP 62 series (62, 62s, 62sc, 62st, 62stc)
GPSMAP 64 series (64, 64s, 64st, 64x, 64sx, 64csx)
GPSMAP 65, GPSMAP 65s
GPSMAP 66 series (66s, 66st, 66i, 66sr)
GPSMAP 67, GPSMAP 67i
GPSMAP 78, GPSMAP 78s, GPSMAP 78sc
GPSMAP 79s
GPSMAP 86 series (86s, 86sc, 86i, 86sci)
GPSMAP H1, GPSMAP H1i Plus
Montana series (600, 610, 650, 650t, 680, 680t, 700, 700i, 750i)
Monterra
Oregon series (200, 300, 400c, 400i, 400t, 450, 450t, 550, 550t, 600, 600t, 650, 650t, 700, 750, 750t)
Rino 600 series (610, 650, 655t)
Rino 750, Rino 750t, Rino 755t