off-line upgrade from OL6.1 to OL8.x is possible?

Hi all:

Wishing a wonderful day!

I wonder if this is possible and acceptable as upgrade path.

One customer has one vms with ol6.1 and want to know if download and ol8x iso image can boot it and upgrade the ol6.1 off-line.

What want to know:

1- is possible? can't reinstall some software although don't know if can be run it on ol8.x

2- is an acceptable and supported (from Oracle point of view) as upgrade path

Customer don't want to use internet to do yum update as upgrade way.

We know that /boot size can be an issue. But if both questions have a "No" for answer isn't worth it finding a way to increase the /boot size (may be clonezilla can be used to address the /boot size).