Admob with other advertising solutions


my name is Anthony, I’m new to this forum.

I have the app published on the 'Android Play Store. As anyone knows, from August 1st
we must abandon the standalone version of the platform and use the Google Admob Play. This involves cutting the versions older than 2.3.3 for Android. I have many users using versions 2.1 and 2.2. I would like to ask yourself the following questions and I would be very grateful if someone could help me:

  1. E 'can be used along with other advertising networks Admob? I go against the rules? I would like to implement Admob for versions up to 2.2 and the rest use other advertising network.

  2. If that is not possible, it is against the rules to implement Admob only for version 2.2 and higher to let the rest without Admob?

Sorry for my english

Thank you all