Estes is a privately held third generation Company started in the southeast. They advertise that they have 27000 pieces of equipment with 13000 employees. Covering 5 regions of the united states. A multi regional carrier that also has links to Mexico and Canada. filling up the rest with a quick statement about air freight, Hawaii, Alaska and of course the rest of the world. Because they are not a public corporation their balance sheet is not public.
Being a third generation company started in the same region as OD Their is probably a good chance that the two families are closely associated, knowing each other. Most the time competing animosities can be swept under the carpet and they probably at least have a friendly associate relationship if not close Friends. Since you cannot see Estes balance sheet you would not know if they are in any kind of financial trouble also not know what the division of assets in the family is or other divisions are.
The merger idea though entertaining to bring forth would be very complicated. the two companies brought together would not fit like a glove. The big benefit that I see in the different business plans is OD may not be as strong regionally as Estes who states that they are a 5 region multi regional carrier. Not stating if they are strong on moving freight in the longer mileage.
The rumor/theory seems very unlikely to me though in the future as their becomes different situations in the LTL sector things like this may happen. How it would be worked out in the end would be a guess unless you were part of the two teams of attorneys being paid the big bucks to put it all together.