That sounds to me as Haiku is using the VESA driver. You can see what driver you are using by running the listimage | grep accel command in the Terminal:
Welcome to the Haiku shell.
~> listimage | grep accel
500 /boot/system/add-ons/accelerants/vesa.accelerant 0x9f8000 0x9fc000 0 0
TEAM 408 (/bin/grep accel):
~>
Actually, no need to go into the Terminal. On the screen preferences, just hover the mouse over the little computer screen and the driver being used will be shown in a tooltip.
To get native resolution, you can (probably) get that with VESA as well. When you boot, press and hold the Shift key (or as an alternative keep pressing the spacebar) until you see the safe mode boot menu. In the video sub menu you can see if you have your screen’s native resolution and select it, not forgetting to go into the safe mode sub menu options and select “use safe mode video” (something like that, can’t recall the exact term).
Are you using netpositive or webpositive? The 2nd is included with A3.
As for the incorrectly identified CPU, create a bug report.