Coming in at a slightly different angle - my entire lab (no longer with us) was out in the garden and a female in season came looking for him
They mated (Tied for the correct term) before I could get to them - I contacted the owner of the female and they came to fetch her
Obviously when the dogs are tied you should NEVER try to pull them apart
YES it did change my dog as anytime he smelled a female in season he would leg it
This wasn't arranged it was something that happened (we live in the country and the female was our neighbour who lived 3 fields away) My neighbour took the female to the Vets and she was given an injection so there were no pups from this little accident
and she was spayed later.
I also received a bottle of wine off the neighbour
So my answer is yes it can change your dog and TBH I wouldn't be happy if both dogs weren't tested prior - sounds to me that your work colleague is looking to make a quick buck