I found a work-around. (my own)... If I install Server 2012R2 it gives me a USB 3.0 platform.  from within 2012 I installed 2008R2 and it worked. I did have to use 2012 one more time into repair/dos window because I forgot to pull over all the 2008 drivers. Once I did that I was able to delete windows.old and now I have a fully functional 2008R2 on an Optiplex 7040.   Sure was easier than all that dism stuff. 
So, trying to install Win Server 2008 R2 on an Optiplex witch is all USB 3.0  Using legacy boot it will boot the installer and NOT freeze at the main screen.  But when it gets to the drives screen it says it needs a driver but won't recognize anything because it needs a driver to recognize the HD and needs a driver to recognize anything plugged into the USB 3.0 ports. I've spent 2 solid days looking at and trying different things including the dell software patcher (the one that uses powershell).  It works great.  Slipstreams usb 3.0 drivers into the server build, but when I boot it ti DOES freeze at the main page because it's taken away the drivers that the keyboard and mouse use. Is there anything else I can try to get this to work?  Am I using the wrong driver?  I've tried drivers that came with the driver update utility.  I've tried drivers from intel's website.  All cause the main screen to be locked up with no mouse/keyboard. I've tried manual usb 3.0 insertion (same result). Any other way I can get this to work? I can use server 2012 R2 (which has 3.0 drivers and hdd drivers and see's the HDD right away, but I'd prefer to use server 2008. Thanks 
MS Server 2008 R2 on Optiplex 7040 (USB 3.0 ONLY) can't get it to work, even 
with all the dism and patching stuff...