See also the official guide:
IMHO, If you have vCenter you can upgrade it first and then use VUM to upgrade the hosts.
PS: the update 1 of 4.1 is now available.
When I did my upgrade, wanted to use VUM but the tech warned me that (at the time ) Update Manager had concerns. I took the path of copying the upgrade file to each host and ran it manually.
I had no problems doing each host this way.