I know you can get this with
sdparm, but it's doubtful it's installed. Might be in
dmesg; the drive model should be in there at least and you'll need to access tech support mode first.
What I would do is just inventory the Dell service tags (and whatever the HP equivalent is; some others can probably assist there) of the servers and use the vendor's lookup tool to see what shipped with the server, what the warranty covers, etc.
Dell tags should be right on the front of the server if rack mounted or top-front if tower.
You should be able to get this from the tech support mode with
dmidecode if it's installed with:
dmidecode |grep -i "serial number" and that might even work for the HP servers.
Another option (assuming you're using vCenter) would be to install the Dell vCenter plugin; it gives you OpenManage-like functionality (including a complete hardware inventory) for your Dell ESXi hosts. I would imagine that HP has something similar.
Probably the best option for not just disk serial numbers, but for ongoing monitoring/management of the ESXi hosts' hardware.