Many years ago, there were certain combinations of locomotives that could not be MU'd. Primarily it was Baldwin diesels that were the odd man out. Baldwin used an air-based MU system as opposed to the electrically based MU system which EMD, Alco and GE used. It was the electrical system that ultimately won that contest and is in use today.
Today, all that MU incompatibility is long since gone. Anything on the road today will MU with anything else. Shoot, we can even MU the 765 to trailing diesels!
As for the use of the word "lashup" I have given up on my quest to stamp put the use of that unbelievably silly term. Every time it is used, all I see in my mind is some diesel locomotives lashed together with a bunch of rope. 
Hey MartyE! It's time to post your lashup picture again! 
