The best option here might be to submit a question to the official FIRST Q&A (
https://frc-qa.usfirst.org/Questions.php) for official help answering this question, as answers here are regarded as opinion unless a proper source is given. If asked there, the answer can be used as a reference for inspection in the event that your team's bumpers are ruled illegal. If you do not feel that asking the Q&A is necessary, it might be a good idea to make a second set of bumper covers that are completely legal in addition to a second set of other materials that can be ready to assemble. Depending on which event you attend, I am sure there will be many teams that would be happy to help your team out if they don't pass inspection.
-JTN
FRC 16