Hi Justin,
I hope you saw the picture:
As you see VIOS 2.2.5 is not even on the timeline. It was dropped off many-many years ago. Even the next version VIOS 2.2.6 is out of support since 3 years! It means nobody tests the newest HMC code if it works with such older VIOS versions.
I can imagine only one reason why you couldn't upgrade VIOS. The reason would be POWER7 or older systems. Everything newer than VIOS 3.1.2 doesn't work with POWER7 at all. If you have POWER7 systems in your environment, NO, you can't update your HMC, because newer versions of HMC don't support POWER7 systems either.
If you don't have POWER7 systems in your environment, upgrade VIOS 2.2.5 to 2.2.6.65 at least and all VIOS 3.1.0.x to 3.1.3.30. It is not such a big deal! It is online in case you have dual-VIO configuration.
Answering your question directly. No, there should be no big problems using 3.1.0.x with HMC V10R2. I still have some VIOS 2.2.6.65 with HMC V10R2M1041. The only problem is that you use not supported versions. In case of any problem you are on your own.
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Andrey Klyachkin
https://www.power-devops.com------------------------------