Salmon mi-cuit is cooked as low as 108F per Douglas Baldwin but this is a "fast" cooking technique that requires only 15-20 min cooking max which is not long enough to render gelatin.
You can render gelatin safely from skin and bones (or whole fish) sous vide for longer periods of time at any temperature at or above 131F.
I would consider rendering the gelatin separately for a long period of time, reserving it, and putting it back with fish possibly done at a lower temperature (depending on what level of doneness you want).
FWIW, the Douglas Baldwin section on Salmon ‘Mi-Cuit’ has a number of interesting tips on low temperature sous vide for fish.
Edited excerpts from: http://www.douglasbaldwin.com/sous-vide.html#YTSalmon
Salmon ‘Mi-Cuit’ - Douglas Baldwin
While salmon mi-cuit is a popular among sous vide enthusiast, it
should never be served to immune compromised individuals. The low
cooking temperatures in this recipe are not sufficient to reduce the
number of foodborne pathogens or parasites. Since the prevalence of
the parasite Anisakids simplex may exceed 75% in various types of
fresh U.S. commercial wild salmon (National Advisory Committee on
Microbiological Criteria for Food, 2008), I recommend either freezing
the fish (below –4°F/–20°C for at least 24 hours) to kill the
parasites or pasteurizing the fish using the times and temperatures in
. . . . . .
Set the temperature of the water bath to 108°F (42°C) for rare salmon,
122°F (50°C) for medium--rare salmon, or 140°F (60°C) for medium
salmon. Then prepare a 10% salt water solution (100 grams salt per 1
liter cold water).
. . . . . .
Cut the salmon into individual servings and vacuum seal. For rare and
medium-rare salmon, cook the salmon for 15–20 minutes. For medium
salmon, pasteurize it for the time listed in Table 3.1. Then remove
the salmon from its pouch, garnish with crisped salmon skin, and serve