The issue most people don't realize, is the bioload having two puffers would produce. A single puffer already puts out quite the bioload, having two large puffers, would probably be over the amount something like a 75gal could handle without giga-filtration and frequent water changes.
Tank issues aside, a lot depends on the individual puffer. There are some puffers that would be an outright no, like the Starry (Stellatus) or Mappa puffer. But like most things in the hobby, someone's already done, and two puffer tanks aren't that unheard of.
What puffer were you considering mixing in with the Immaculate?