It CAN work, because others have succeeded at it, but that doesn't mean it will automatically work for you.
First of all, it take agreement on everyone's part - and not just agreement, but real commitment to it.
Secondly, just because a relationship is open doesn't mean "there are no rules and everything goes." People have to understand what "crossing the line" means and that will be different for every couple. For some, it will mean, "You can do it with others - but NOT in our marital bed (or house)." Or, "You can do it with others, but only when one or the other of us is unavailable." In other words, it might not be OK to leave your primary partner sitting alone at home while going out to prowl around.
So, bottom line, this is like negotiating a complex contract. You really do have to sit down and go over all the "parties of the first part not doing things to the parties of the second part" in order to make sure that everyone understands and agrees to what is OK and what is not.
And just like all contracts, some will work beautifully, some will have a few snags that need to be smoothed out later on, and some won't work at all.
Best of luck to you both.