55 gals - not a chance. It MIGHT be possible to keep A male with several females in there, provided the females had plenty of cover so that he did not constantly harass them to mate, and there were several (I vote eight absolute minimum) so he would spread his attention out. It still seems a bit silly to me - buy the 55 gallon tank, put some females in there, and then have a nice peaceful community. It's not hard to find a corner to tuck away a 5 gal somewhere for the male/s.
As to keeping two males - I seriously doubt that you would pull this off. The whole thing about bettas living in puddles is crap. It's propaganda designed to make the public accept keeping them in drinking cups. It IS possible for them to survive in buffalo footprints or whatever, and it does occur in the wild, but it isn't as common as people are told. Generally bettas live on rice paddies or other large swamps. There ARE many males in these areas. So it WOULD be possible to keep multiple males in the same tank without dividers - but the tank's surface area would need to be at least that of a small room IMO. It woudln't necessarily have to be deep.
The most important thing to remember is that by putting these fish in a tank that is smaller than their natural habitat - a big shallow marsh - you are preventing, to some degree, their natural behavior. In the wild if a male encountered another male and did not wish to fight for territory he would simply leave. By keeping him in a relatively small tank - even a 55 gallon tank - you would be denying him that option. The other betta will take his presence to indicate aggression, and they will proceed to beat the living crap out of each other.
The males in the wild do not seek shelter from another male, because to remain in his territory - even cowering behind an object - is still a challenge... it implies "I'm gonna wait till your back is turned."
Now I did assume that by '55 gallon tank' you mean 'roughly rectangular glass box with capacity of 55 gallons'. 55 gallons would PROBABLY be enough space - if the water was only a few cms deep and the 'tank' had a vast surface area to provide the two males with separate and adequate territories so they would have no need to fight. If you did manage to pull off the incredible feat of having them not fight at all, adding females would be very stupid indeed, as you are then giving them a motive to prove their superiority over the other betta (namely reproduction).