Maybe - maybe not. This thing was taken with the microscopic lens. That's a pretty smallish valve. Also take a close look at the business end of Opportunity's rock abrasion tool photo below. It or another tool could have left an impression in the soft soil.
As much as I do believe that NASA - JPL - et-al cover a bunch of things up and air brush lots of things out I also must use my God given brain to try and figure out when someone jumps the gun and starts seeing things that aren't there. Dhaboo7 has a proven track record of doing just that and as such his missives automatically trigger my caution goggles to the "on" mode.
http://mars.nasa.gov/mer/gallery/press/opportunity/20040202a/2_rock_abrasion_tool-B009R1_br.jpg
!! FOXTROT JULIET BRAVO !!