Interesting debate.
The principal difference between a pork pig and a bacon pig is that you want a larger pig for bacon. This is because if you take the pig off too small the loin (which make the back bacon) will have a good "eye" but no "tail". So you get a round rasher ! You also get a larger joint for hams.
However for pork joints, you generally want a smaller pig, as otherwise the leg joints don't cut into managable sizes and still get a good covering of skin for crackling.
Hence pork - smaller, bacon larger is the general principal.
You can achieve this three ways.
The first is to have breeds that tend to grow grow to the size, so larger breeds will be easier to grow for bacon. Smaller breeds such as the middlewhite are used for pork (which is why the middlewhite is known as the London porker).
The second is to simply grow your pig to size. If you are smallsacle, then keeping your pork pigs for say 6-8 months, and your bacon pig 8-10 months gives you good size pork joints (but not too big) and good size bacon by keeping longer. Clearly if you are commercial, you wouldn't want to waste time doing this so select for breed.
The third (a sub bit of the second) is a to select your weaner within the breed for what you want it for. So when choosing say your saddleback, look for a squatter more muscley pig for pork with chunky legs, and a longer pig (the length of back determines how much bacon you get - longer back more bacon!) for your baconer. Then simply grow to size.
So the asnwer is yes you can use any breed to make pork or bacon, and you can take pork or bacon from any size pig. However the tendancy is to want smaller joints and larger bacon, so size makes that difference. But absolutely no reason why you should take a pig off and use the legs for joints and the loin and belly for bacon.