There is "Run Always" checkbox under "Advanced" for Warnings plugin. It allows count error/warnings in case when build fails. However, the trend graph does not display graph for failed builds except last one. On my trend graph I got builds 1-22 and then 39. Builds 23-39 were failed builds but 23-38 did not make it to the graph. I can see that errors were in fact counted when inspecting individual builds.