Of all the levels in that game - Hoth is pretty much the best fit for PS2 architecture - landscape rendering is one of the poster-child examples for what VUs were designed to excel at, all the dynamic lighting is vertex based, object-space shadow maps worked really well on PS2 GPU (although it'd probably improve quality compared to base-game to switch over to shadow volumes), and texture load per-frame is minimal as there's precious little on screen outside of snow at any given point.
Oh and it's 16bit frame-buffer on GC, so 'maybe' color depth could even be improved - but that's a toss-up, might be worth the tradeoff for other non-performance reasons.
Now - would it still run 30-60fps in split screen, that's a more interesting question, but given the relative simplicity of the game simulation in RS, and the fact we're not rendering any kind of complex level topology (texture or geometry wise), probably?
And sure - it's mostly rigid geometry (no skinned animation, even on soldiers by the looks of it), which helps out GC - but that also helps out every console, as skinning wasn't free even on the XBox.