They should have access to a 'poultry' mix additive as well... The difference between 'chicken feed' and 'hog feed' is mostly just what supplement mix they dump into their base mix...
It's really hard to say if adding the hog minerals will balance it out without a lab analysis, but it certainly won't hurt...
Also chickens will 'sustain' on a slightly inferior feed, they will just eat more to compensate so you feed conversion lessens, bumping up the protein as you suggest also helps as chances are greater they will get the proper balance...
You can try getting 500 lbs and see how the birds do on it, I have no idea what their 'hog' mix is so I would recommend you pick up a bag of Diamond V and either have them mix the appropriate amount (or just dump in 10 lbs and call it a day) in or simply mix some into the feed your self... When I supplement for my peafowl and ducks I use the Original XP version and just sprinkle a handful into their feed each day, no precise measurement needed...
There are several different Diamond V mixes,I use the 'XP Original' version personally as that is what my feed store carries you could use that and have them dump a few pounds into your 500 lb mix and you will be well on your way towards a balanced diet, or as I do just mix some in yourself...
http://www.diamondv.com/products/original/
I have considered having my feed store order me in a bag of the newer 'XPC Ultra' version if it's not that much more costly and giving that a whirl as it's super concentrated...
http://www.diamondv.com/wp-content/uploads/productprofile_xpc-ultra.pdf