Pretty sure most of the grognards have their favorite system or they wouldn't be grognards, they have plenty of options that will give them a more grognard like experience than D&D Basic, they have the rule books on their shelves and plenty of OSR clones available.
But sure some will they exist, but I would bet they are a very minor minority of people playing D&D 5e in 2015.
They also might be looking for more people to game with, and be willing to compromise a little more in game mechanics for a bigger pool of people.