Yes, you need to set the pin addresses on the RTC (assuming the RTC has an address pin) as this sets the address your software will use to talk to the RTC.

Whether you use software to bit-bash the i2c via port pins or whether you use the internal hardware of the aduc831 is up to you - the internal hardware i2c just makes the software a little easier. In your application there would probably be little performance difference between the two methods. If you already have sample code that bit-bashes the i2c, use that if you feel that makes your job easier.

Given a choice - I would lean towards the hardware in the chip. Your mileage may vary!