I honestly can not think of one situation where I have been an opponent. So how do I function as a partner?
The concept of training partner is one of the principles I teach in my Introduction to Jujitsu course. Every technique requires a partner to train with. Every technique is done on you as many times as you perform the technique on someone else. If you go hard and are abusive you either will not be able to find anyone to train with you or you will find someone who will be even more abusive to you (Cool, you want to see who hits softer. Dogs, I guess you win.)
In the dojo we have an Uki / Tori relationship. Uki receives the technique (often the attacker) while Tori executes the technique (the defender). Without Uki there can be no Tori. To communicate the concept to my students I sometimes use the terms trainer or coach for Uki. As the coach Uki must feed Tori something substantial to work with. As Tori develops skill in the technique the trainer changes the attack (while maintaining the intent of the art) to stretch Tori's ability to respond. On the other hand, if Uki were to come at Tori in an "opponent's" mind things would quickly escalate out of control and technique would become lost to instinctive survival responses.
At work there are two groups that don't get along to well and spend considerable effort with CYA and collecting data on the other's shortcomings. I guess I do see an opponent situation here :(. Should they follow through with the lip service they give to team work and seek ways to help one another the stress level might reduce and I'm sure the product would get to market a little sooner with higher perceived quality.