This is not a visibility to the compile phase issue, I don't think.
Rather it's related to the hosted mode embedded Tomcat not seeing the
file.
Maybe I am confused, but I think we are talking hosted mode Tomcat
doesn't see it, since you are using gwt:gwt. In this case it's a
tricky one, the hosted mode tomcat gets the classpath and web.xml from
GWT-Maven, but it doesn't get other resources unless they are
specifically added.
I already have an issue around to try to make this work more smoothly
in hosted mode -
http://code.google.com/p/gwt-maven/issues/detail?id=82
- but for now you may have to use AntRun or such to copy the file over
to the hosted mode location. (It's not the final WAR that is at
issue, or the target, it's the hosted mode "tomcat" folder - a bit
more complicated, unfortunately.)