No. At least if I understand your question correctly.

GVM can be set to 'fullscreen' on/off. In 'on' mode it will use the full N800 screen, but display the PalmOS interface in 'portrait' mode inside that screen. In 'off' mode it will display the same PalmOS portrait mode turned 90 degrees, i.e. in N800 portrait mode. But then it doesn't occupy the whole N800 screen.
There's no current way to display the PalmOS screen in landscape mode (landscape as defined inside a 480x320 display as can be done on a T3/TX/T5/Lifedrive device).

I'm attaching a couple of screenshots to display the two possible modes.