Thanks,
Yes , for an applet with hardware accelerated you must signed your applet(because dll). And it's more interresting use a cetificate signed by trusted authority.
In World java 3D you have two binding OpenGL but it's just a "binding" for openGL not an engine 3D(SceneGraph): LWJGL and JOGL are very good, many games use this apis(notably wakfu).
But the Big problem in Java you have not 3D "engine professional" , just open source project like Java Money Engine . This engine is stable but you have lot of issues with importer/loader objects.And the skinning animation are not really performant.
In theory , it's possible use your engine with Java Native Interface but it's lot of work , you must rewrite all interface public methods.