Yes.  The inspectors will probably be pretty nit-picky on the bumpers this year, since FIRST placed so much emphasis on them.  You need to build them exactly as the rules specify.  Good luck!

techalex wrote The bumper diagrams in the manual are simply guidelines. We didnt put the metal last time and they did not care, but of course things change from year to year and inspector to inspector.

Note that the instructions in the manual are not guidelines, but actually specify rather specifically how to construct bumpers; because they are meant to protect the robots and the field FIRST is fairly picky. Also, considering they're outside of the robot weight limits, they're fairly limiting on how you make your bumpers. But yes, there may be some variation between inspectors. In general, they probably won't mind so much if you leave something like this off; you're more likely to get cited if add things to them or use different materials.

--Ryan