I am using Gradebook2 for Sakai, developed using GWT. This tool is not loading in IE8 (without compatibility view) when I set the property sakai.X-UA-Compatible=IE=EmulateIE9.
When I enable compatibility view this tool is loading properly even though I set the property sakai.X-UA-Compatible=IE=EmulateIE9
It's possible, for some reason that having IE=EmulateIE9 alone is getting IE8 to fall back to the wrong setting. That's not unusual as described here.
Maybe you need something like
sakai.X-UA-Compatible=IE=9; IE=8; IE=7
as mentioned on this related article.
I think that having edge would work but the you probably also want IE10 and IE11 to fallback to IE9 compatibility mode as then you might see other issues in those browsers.