Well there are a couple of problems...
1. Sven Co-Op (or at least I think thats what you are talking about) doesn't work on half life source, it only works on the original half life. freeman's mind is on HL source.
2. Why are they having a conversation? It just seems weird considering you only see freeman at one part in Opposing Force, not to mention Gordon would most likely kill him on sight.
3. It seems far too late in the game to have this added :S but I wouldn't mind having the "Get back here you big orange f*ck" when Gordon is teleporting to Xen, though.