Can I use a USB 2 Pin Adapter (Iphone Charger) to Power the Arduino in this setup?
Yes.
(In "Series" with the Heater if you will)
What?
The Arduino has to be electrically isolated from the power line and the USB power adapter will take care of the isolation on power-supply side.
I assume you are using a relay to switch the 220V heater-power and relays are isolated.
I don't want to have two power Supply's
If you're using a USB power supply (5V) you'll need a relay with a 5V coil. (And, you'll need a relay driver because a relay coil requires more current than the Arduino can supply.)