Is there any difference to which hand I equip two weapons to? I've switched around the two weapons I currently have equipped and my DPS remains the same. Does this mean I can equip whichever weapon in either hand with no change in damage output?
In most cases it does not matter which weapon is in which hand, although you have to keep in mind that only one will be used in most attacks (except for skill gems that explicitly use both weapons at once of course).
In regard to Main-Hand/Off-Hand calculations there is no such thing as an Off-Hand handicap or anything like that.
According to the game wiki, weapon usage is alternated with most skills. But since only one weapon will be used in most attacks, only that weapons on-hit modifiers will be applied. This might be relevant when you heavily rely on modifers like "life gain on hit" or mana leech, especially when using one of the few skills that explicitly only use the main hand weapon for attacks.