Pork Souse can be several different things. But all of them are closely related, and mostly all of them are made in the southern US.
The term can be used in the American south to mean pretty much the same thing as "head cheese" (aka Pork Brawn) would mean elsewhere. "Head cheese" labelled "head cheese" is available in the American south, but the most it will probably contain for flavouring is onion and garlic powder.
If the head cheese is called Souse, though, it is more likely to have some additional flavourings added, such as lime juice, red peppers, chopped cucumber and onion, pickles and /or relish. It is particularly more likely to have these flavourings in it if you are buying it ready-made in stores. And, it may sometimes contain beef as well as pork. It's ready to eat, and needs no further cooking. For the catering trade, it is sold in tubs and large plastic-wrapped blocks; direct to consumer it is sold in much smaller plastic wrapped packages in some kind of loaf form, so that it can be cut into slices. It can be used as sandwich meat, or as a main course. It can also be covered in some kind of flour or meal and fried up.
Hot Souse is Souse that will have hot red peppers in it, giving it a spicy taste. Souse is often labelled "hot" or mild." In Louisiana, "Hot Souse" will often also have crawdads and fish parts in it, and be very spicy.
The other meaning of Pork Souse in the American south is pieces of cold pork served in a sauce. The slices of meat may be marinated in some lemon juice for a few hours in the fridge, then served with cucumber and some kind of dressing.
On some Caribbean islands, Pork Souse is more of a hot dish. It's made like head cheese, but instead of being allowed to stand and congeal, it's served warm in a bowl like a thick soup.
'Good bread and good drinke, a good fier in the hall, brawne, pudding and souse, and good mustard withall' (Thomas Tusser 1573).
Literature & Lore
"Souse" in English is a verb that means to dunk into a liquid, cover with a liquid or to steep in a liquid. "Souse" is sometimes also used to describe the brine liquid that pickles are steeped in. A "souse" is sometime who drinks too much, perhaps picking up on the thought that they might be pickled from within.
Musically, "Hot Souse" is a mixture of blues with jazz, rhythm and blues and soul mixed in.
Some people use the phrase "Hot Souse" as a way that they feel is clever of trying to capture how an American southern accent says "hot sauce".