I am working on an application that through which I want to sell some event Tickets.
Can I use PayPal for this purpose, and will Apple approve the app using other t
Well I think that depends.
Although I was sure Apple wouldn't allow anything else than In-App-Purchases, I do know at least one app in the german appstore, which allows you to purchase tickets to a movie theatre within the app. They offer payment via credit card and a number of other services, IAP isn't even available.
They made it to the store somehow, so I'd suggest you go ahead and talk to Apple beforehand and find out whether they'll approve your business model or not.
Maybe they approve other methods of payment if the purchase consists of 100% real-world objects or services and does not change the behaviour or content of the app itself.