I figured out the problem. The Maven Integration for Eclipse plugin is attempting to write a file to the JBOSS_HOME/standalone/tmp directory, even when the temporary deploy directory is specified elsewhere. I caught it trying to write this file:
/var/cache/jboss-as/standalone/tmp/tmp3463101666163615035.MF
Manifest-Version: 1.0
Built-By: fedora
Build-Jdk: 1.7.0_b147-icedtea
Created-By: Maven Integration for Eclipse
If I change the ownership of the tmp directory to the current user, the deployment succeeds (all the files are copied into the specified deploy directory).
A quickfix for this problem is to make this tmp directory world writable (i.e., chmod 777) or to add the current user to the jboss-as group, since the directory is currently setup as:
drwxrwxr-x. 5 fedora jboss-as 4096 /var/cache/jboss-as/standalone/tmp
So now we know. Look for the code that writes this temporary file.