I ended up creating a separate profile to run tomcat and skips the goal execution:
<profile>
<id>foo</id>
<build>
<plugins>
<plugin>
<groupId>de.saumya.mojo</groupId>
<artifactId>gem-maven-plugin</artifactId>
<executions>
<execution>
<id>compassProcessSource</id>
<phase>none</phase>
</execution>
</executions>
...