What is you are making payment on the car and owe the dealership for something else can they repossess the car?

Yes and No.

By "they", I'm guessing you mean whoever technically owns the car that you are making payments on, and is most often a bank/credit union. If you owe the dealership for a repair bill or something, it is separate from your car payment, and would most likely have no impact on your lease, therefore not be repossessed.

On the other hand, if you owe money because you didn't pay your insurance (in a State where insurance on a financed vehicle is required by law), then the lender will furnish insurance from a company they choose and add the cost of each month's insurance payment you missed, plus any months adding up to 6-months to a year right to your loan including interest and all. So while you could go a couple months paying the same amount you've been for the car, not paying the extra $100-$200 a month on the same bill will quickly get them to send the repo guy.