If this is a new case, does the manual or the manufacturer's website have any information on it? if it didn't originally come with standoffs, I would assume those little hills were meant for that purpose.
I would look through the manual if it came with one, and then hit up the website and see if you can find anything -- otherwise, try this
Mount the motherboard on these hills (don't power it up) and see if it matches up to your backplate on your PC, if it does, you're safe, if you were to add standoffs it would raise it up to where it probably wouldn't match up.
Hope this helps.
Also, you could probably rig up some thin, non conductive plastic washers or something for the mobo to sit on, probably.