No. You can only use one account at a time, and once your device becomes associated with an ID it cannot be changed to another ID for 90 days. Note: this doesn't mean you can't sync media purchased with different IDs to your device. You can do that as long as your computer is authorized for the IDs (in Store>Authorize this Computer).
Can you use 2 iTunes accounts on one ipad
Yes. Log out then log back in with the other account to make purchases.
Note that randers4 explanation simply means you cannot download previous purchases on the other occount from the iTunes store.
You can sync the iPad to your conputer and put all items in your ibrary (from multiple iTunes accounts) onto the iPad.