Simple but not so simple.
Answer: No, BC is not necessary for an applet.
Yeah this is possible.
Here are few quick samples to look at in Siebel Tools
Applet:About SRF Applet
Class: CSSSWEFrameAboutCDFDialog
Applet:About Siebel Applet
Class: CSSSWEFrameAboutSiebelDialog
Applet:About Record Applet
Class:CSSSWEFrameAboutDialog
Applet:Change Records Popup Applet (SWE)
Class: CSSSWEFrameChangeRecordsPopup
Applet:EAI Web Service Export Popup Applet
Class:CSSSWEFRImpExp
--------------------¤OptimusPrime¤----------------------------------