if a yum repo is disabled for the distro, hwcert-backend plan will complain once (and only once).  Running hwcert-backend plan again, as well as running tests which depend on the missing rpm does not cause hwcert-client to attempt to download the missing packages.  No complaint is given about the missing packages, beyond the initial `plan`

This means that if a repo is initially disabled or temporarily unavailable, the hwcert-client tests fail even after the repo is made available again.  So it's not really handling the yum error.  It's simply ignoring the error once, and then never running anything which might trigger it.

I'm not sure what you're asking.

And "hwcert-backend plan" will ask everytime a new plan is created (after hwcert-backend clean).

hwcert-backend plan won't ask when it is re-run to check for hardware changes on an existing plan.  We could have it ask and warn every time (both new and re-check).  Is that what you're asking?   It seems as though that might get tiresome having it point out the missing packages repeated every cycle.

Also, "hwcert" asks each time following submit and/or save of the current test results.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

http://rhn.redhat.com/errata/RHBA-2014-0532.html