As mentioned, ALUA is supported on all current ESXi versions.
You can check the current runtime status of LUNs and whether they are being accessed with ALUA by checking if the VMW_SATP_ALUA SATP claimed the storage device.
You can do so via the GUI or more verbose from the ESXi shell like this:
# esxcli storage nmp device list
naa.600508b40010439a0000b000003b0000
Device Display Name: HP Fibre Channel Disk (naa.600508b40010439a0000b000003b0000)
Storage Array Type: VMW_SATP_ALUA
Storage Array Type Device Config: {implicit_support=on;explicit_support=on; explicit_allow=on;alua_followover=on;{TPG_id=1,TPG_state=ANO}{TPG_id=2,TPG_state=AO}}
Path Selection Policy: VMW_PSP_MRU
Path Selection Policy Device Config: Current Path=vmhba2:C0:T1:L2
Path Selection Policy Device Custom Config:
Working Paths: vmhba2:C0:T1:L2
Is Local SAS Device: false
Is Boot USB Device: false