Try to add the EAR Libraries classpath container to your ejb and war projects (right-click the project, select Build Path>Configure Build Path..., select the Libraries tab, click the Add Library button and add EAR Libraries).
You will get the following line in project's .classpath:
<classpathentry kind="con" path="org.eclipse.jst.j2ee.internal.module.container"/>
I suppose m2e-wtp would have to add this container automatically to the projects included in an EAR.
This is a WTP container that sets EAR dependencies to an EAR module.
WTP sets this container when adding some WTP module to an EAR.