SilkTest supports Oracle Forms applications as it would any Java applet that consists of custom classes.
All children of the applet will be seen as CustomWins, with native class names such as "oracle.ewt.*" and "oracle.forms.*". You will need to declare winclasses for any classes that you plan to use, and you will only be able to interact with classes via scripting. For more efficient declaration of classes, use the CaptureAllClasses() function instead of using Record Class to record each class separately. (See the on-line help for information on CaptureAllClasses().)
As with any application consisting of custom classes, if there are objects that SilkTest does not see, try enabling "Show All Classes" to see if that exposes the ignored objects. If so, then you should add those classes to the [ClassList] section of "extend\JavaEx.ini". Disable "Show All Classes" before recording window classes or declarations.