Hmm. Rereading this
does mean that, like gogalthorp says, you should be able to install MBR. I don’t have access to any computer with such a dual/combo choice. My computers are Legacy or UEFI. Period.
With W8, you did install using MBR. I wonder if you made any selection during W8 install in that regard? With openSUSE, it seems that you do not have any choice. It detects UEFI, and that is what is being acted upon.
I wonder if openSUSE could be forced to do MBR install in such a case? That require Linux competance outside my current level. Anyone?
The above also means that you only have two choices: Pure UEFI or a UEFI/Legacy combo. If neither OS can be forced in any direction, and you need to go with what is being automatically detected, then your only choice is the immediately most bothersome: Pure UEFI (or no dual boot. In this regard, other distros may differ from openSUSE in what is detected during installation. I don’t know.)
However, there may be still another possibility:
In the UEFI world, Legacy BIOS mode is often dubbed CSM - Compatibility Support Mode. If you select UEFI mode - does an option called CSM appear somewhere then? If that is so, you still have the choice between pure UEFI and pure “Legacy”, and the choices I describe above still apply. If not, you need to go with UEFI and reinstall W8, or skip dual boot with openSUSE (unless it can be forced to MBR during installation). This I cannot test out for you, as I do not have any equipment with the necessary features to do that.
I’m getting curious as to what you end up choosing. 
Good luck!
dayfinger