We currently run our web adapter on windows server 2008 r2 without any issues. maybe you could describe more specifically what you are concerned about if you require more information. cheers.
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for what's its worth I have successfully added your URL to my test geoportal (v1.2.2) administer->add-> network resource-> selected arcgis protocol so i guess the problem is not on your side. sorry i cannot help you more!
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