No, it doesn't use PBOs for texture data. It uses the "normal" way to upload textures. It doesn't use VBOs either let alone by default. It has two different render paths, one that i call hybrid path (which is default) that uses vertex arrays, but in a slightly different manner than you would expect. The other path is the compiled path (enabled by calling compile() on an object) that uses vertex arrays and display lists. I played around with VBOs, but they weren't any better than display lists for what jPCT is doing.
To use jPCT in an applet as a software renderer, the 240kb jar is all you need. If you want to use OpenGL in an applet, it's a different story.