Nope. Not necessary but apparently routinely recommended. If you are cooking the bones for a full day you are getting out what you want to get out. Try cutting the pieces into 2-3" chunks to expose more of the bone surface and add some lemon juice instead of vinegar (the acid is the key; not specifically the vinegar). I kind of like the thought behind some acid being needed to extract more minerals from the bones but I've seen some say it isn't necessary... cook the hell out of them, though.
If you used white vinegar that could have been the problem. What do you mean by nasty? Just the taste? Apple cider vinegar is a better choice. Or the lemon juice.