I did that and restarted AIDA64 and it doesn't show memory temperature. I also tried unchecking it first, then restarting AIDA64, then checking it again and then restarting again -> it still doesn't show memory temperature!
(Running AIDA64 5.99.4900 on an ASUS Maximus X Hero (BIOS Version 1801), memory is 2x 8GB DDR4-3200 from GSkill (model number F4-3200C14D-16GTZR). According to GSkill, those models *do* come with a temperature sensor!)
Look at screenshot #2: