Looks like one other possible workaround is to (temporarily?) mark the dependency as having 'provided' scope. Or to ignore the maven-war-plugin executions (as seems to be the default now in the m2e-wtp lifecycle mapping metadata) - which again seems to defeat the purpose of using this in eclipse to automatically update things.
I'm surprised that no one else seems to be running into this with eclipse (or that disabling workspace resolution or ignoring execution appears to be acceptable for those who are).