On the other hand, we are not using Enterprise Plus license and thus not using Host Profile at our site
Using Host Profiles might be one way to hit the issue. Other cases might cause this behavior like yourselves.
2) Do I need to enter maintenance mode for the changes ? Is it necessary for me to restart the host ?
No. I tried on my setup and it does not require maintenace or reboot required.
3) Just out of curisority, there is no vmk0 in ESXi2, even though we change the vmk2 for vMotion, how can Mgt get vmk0 ?
Well, that is a tough call. Either you can decide to live with vmk1 for management, or try to look at esx.conf file and locate the entries of vmk which is used for management and find out where is vmk0 and assign the same.
If is there no display of vmk0 anywhere in esx.conf, then, I would not recommend changing back to vmk0, since the MAC entries and helluva stuffs might get mixed up.
If you do have a valid support, you can raise a support request with VMware on this issue to ensure that it does not happen to other servers and the user should not go through the trouble of binding the vmk to specific portgroups.
Happy to help,
zXi