I kinda thought so but I can't imagine it being in any way practical.
Most people use a desk for the keyboard etc. The screens are designed to work within the same level you use the keyboard. If you are using a desk, why would you want to use an arm mounted monitor?
Why drill holes into your wall if you don't have to? Especially since you will need to find the wall studs to ensure that the drywall doesn't fall out and drop your monitor on your head. Sometimes the wall studs aren't so cooperative in their locations.
WW