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While this is a common idea among those that don't want to have a permanent rooster, it is an idea that comes with several potential issues that make it an unwise choice. First, yes, there will be issues in integrating him to your flock and back to his own flock that can be quite problematic. Secondly, there is the issue of bio-security -- moving birds into and out of flocks is a great way to spread disease. Even seemingly healthy birds can carry diseases and birds moved from one location to another are exposed to new/different "things" in the environment that can cause illness in them or the birds they go back to. To try to avoid this issue you would need to do a proper quarantine which adds a minimum of 30 days to the move into your flock and move back into his own flock - and the quarantine process itself can be stressful on the bird being quarantined. Once he is introduced there is a period of time that will need to pass for the hens to begin to accept him and his advances - which can vary from days to weeks....and from that point another couple of weeks is generally needed to see good, consistent fertility rates in the eggs being produced. This is in no way going to be a timely process to get to the point of having eggs ready for hatching.
An alternative would be to simply source fertile eggs from your friend's flock and hatch those -- this avoids all the issues above and still gives you eggs to hatch.
The other consideration is that in hatching you are going to end up with a good percentage of male chicks -- as you are no inclined to have a male of your own, what are you planning to do with those chicks?
