dosbox has some strange limits in the code for limiting number of axes and hats.
But if you set joysticktype=4axis all four axes should work (at least they do on normal joysticks/pads). I think xbox360 pad has 6 axes. Each trigger is a separate axe, and are detected as axe first and axe second.
left stick is axes 3rd and 4th.
So right stick will not work as the right stick is axe 5th and 6th
Although i heard that you can configure xbox pad (in its drivers configuration panel) to use its triggers as only one axe (not two separate axe), or as buttons. So if you configure them as buttons right stick should work.
And if you configure them as only one axe, they will be axe first, left stick will be axe 2nd and 3rd, right stick will have only one axe working (4th).
Can you confirm what i said?