jmod didn't fail when installing a jdk module while its dependencies are not installed. However, jmod fails when installing the classic com.greetings example when org.astro module (its dependence) doesn't exist.

To reproduce, cd to a jdk build directory:
$ jre-base-image/bin/jmod ls
jdk.base@7-ea
jdk.boot@7-ea

$ cat tmp/modules/src/jdk.rmi/module-info.java
module jdk.rmi @ 7-ea {
    requires public local sun.rmi @ 7-ea;
}

$jre-base-image/bin/jmod install modules/jdk.rmi/classes jdk.rmi
----> expect this command to fail but it succeeds as sun.rmi module hasn't been installed. Looks like its dependencies are not checked during installation.

$ jre-base-image/bin/jmod ls -v

jdk.base@7-ea
  requires local public jdk.boot@=7-ea

jdk.boot@7-ea
  permits jdk.base, sun.charsets, sun.corba, sun.deploy, sun.desktop, sun.enterprise, sun.httpserver, sun.instrument, sun.jarsigner, sun.jaxws, sun.jdbc, sun.jmx.connectors, sun.jndi, sun.jndi.cosnaming, sun.jndi.providers, sun.kerberos, sun.langtools, sun.legacy, sun.localedata, sun.logging, sun.management, sun.prefs, sun.resources, sun.rmi, sun.scripting, sun.sctp, sun.security, sun.security.compat, sun.security.misc, sun.security.tools, sun.servicetag, sun.smartcardio, sun.sunec, sun.sunjce, sun.sunpkcs11, sun.xalan, sun.xml, sun.xmldsig

jdk.rmi@7-ea
  requires local public sun.rmi@=7-ea