I visited Salvador in July 2018, probably the best place to check this tentative site as 5 of the nominated forts are in that city: Santo Antônio da Barra Fort, Santa Maria Fort, São Diogo Fort, São Marcelo Fort and Nossa Senhora de Monte Serrat Fort. All forts are managed by the army, but is possible to visit all of them easily, except for the São Marcelo Fort, currently closed after a restoration (as far as I know, they still don't have a decision about the new use of the building). None of the forts belong to the WHS Historic centre of Salvador. I did the best I could to take a look at the 5 forts, and here's my impressions about them:

Santo Antônio da Barra: The most famous of all 5 forts, it is usually called just Barra lighthouse (Farol da Barra), because there's a typical striped lighthouse inside the fort. It is very imposing, and settled in a nice place, with beautiful views of the coast and the nearby Santa Maria Fort. The entrance is not free, as it functions as the Nautic Museum of Bahia. The exposition is ok, it must be more interesting for people who likes ships, not much my case. The visitors can also go to the top of the lighthouse. It is a must-see if you're in Salvador, a typical fort, very well preserved, and easy to reach, as it's located in a very touristic area.     

Santa Maria: From Santo Antônio da Barra you can reach this fort by foot, as well as São Diogo. It is a very pleasant walk along the Barra beach. Santa Maria is a small fort, very simple compared to Santo Antônio da Barra, but I really like it, it is very well conservated (it was restored in 2016) and the location on the beach is beautiful (picture shows the view of this fort). Right in the entrance there's a screen showing the locations of all forts of Salvador and some history of them, a nice detail. Entrance here is free, except for the exposition space, that is very small, and don't show much of the structure of the building (the museum area of Santo Antônio da Barra does), so if you're interested only in the fort, you can pass the exposition, here about photographers of Salvador. If you do like photography, it can be interesting, but you will not see many photos hanging on the walls, it is very digital.    

São Diogo: This one is very related to Santa Maria because they were constructed at the same time. It is also small and simple, but the location, on the slopes of a cliff, makes it a strange fort, it doesn't look much like one. It gave me an impression it's just some kind of layered,  narrow squares. The views of the bay are the best part. Entrance is also free except for the exposition space, here dedicated to Carybé, a local artist. Like in Santa Maria, it's a digital exposition, don't expect to see his real work. 

São Marcelo: It's probably the most interesting one, but also the most complicated to check, even when it is open to visitation: it is totally surrounded by the sea, so it's only possible to reach there by boat. Its circular shape make it looks like an island. It is not very far from the land, but there´s no great views from the coast. Best way to see it is from the Upper old city of Salvador (part of WHS area), in Tomé de Souza square, next to Lacerda Lift (check the porch of Rio Branco palace, entrance is free), or from the Nautical terminal, close to Modelo market. The problem to check it from the terminal is that I think you can't go inside the area with the views of the sea and the fort if you're not going to some boat trip. I'm not sure about that, I don't remember well because the terminal was crowed. The fort is close to the terminal, so as I made a day trip to some islands I was able to see the fort closely, from the boat. I think it's the best that can be done while it's closed.

Nossa Senhora de Monte Serrat: A more distant fort, in Ponta de Humaitá area, a not very touristic area. I remember only a few people there. The fort was closed, but I think it was because the time I went, around midday. I don't think it is closed for renovation or something like that, it was just bad luck. Anyway, I was satisfied to check it just from outside, because it is a peculiar fort, with huge cylindrical towers, instead of the usual little lookouts of the bastions. It is a small fort, like Santa Maria, but the towers and the long staircase of the main access make it imposing. Conservation, however, could be better.