As it turned out, SWT 3.5 had an error that prevented it from responding correctly to Info.plist, that OSX required to hide the application. This bug has been fixed in SWT 3.6, and with the release of Eclipse Helios today, I believe that SWT officially officially has version 3.6
To reach the hidden icon, at the top of your info.plist file, you just need to add the following line:
<key>LSUIElement</key> <true/>
mystro
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