Can i test native ios app with Jmeter using Simulator? Also, my app requires login. If not what is the best tool i can use for that?
If you want to measure your application performance JMeter won't help you, it's a load testing tool which acts on a network protocol level.
So if you want to collect application-side performance metrics and detect slow parts of your application it's better to use Instruments (comes with Xcode), see i.e. How to find and fix slow code using Instruments article for more details.
JMeter can help you to simulate hundreds or thousands of iOS application users concurrently accessing the backend or database, but this is the test against the backend, not against the application. If this is something you're interested in you could record your mobile application traffic using JMeter's HTTP(S) Test Script Recorder and once done replay it with increased number of virtual users to see how your backend handles the load. Check out Load Testing Mobile Apps Made Easy article for the overall concept.