I have had the same idea but have not tried it out yet. I am currently working on a full Vog, but right now I'm at Vog Cap & Ash Coat + Wise Owlite Shield. The other day I picked up a Deadshot Mantle recipe with the idea of trading it out with my Sinister Skelly Suit for Undead/fiend work & have been considering it for FSC.
At my current skill/experience level I think I might be better off with a full Vog though. My first FSC run was in Vog/Ash and it went great, but I was with a very solid party. Since then I have not had much luck either solo or PUG (solo went better...).
The main damage types in FSC are Normal/Fire/Shadow/Elemental. Honestly though of these I think Normal and Fire are my biggest concerns. Fire mostly from derp or lag miss-steps and normal from off-screen Slag Guard hits. With that in-mind Volcanic Plate Armor could be a great choice for FSC. As a sword user I'm just not excited about having to overcome the ASI nerf that comes with Plate armor though.
Seems good to me, the only little drawback is the lack of fire resist on Deadshot. Maybe you could try to get some fire UV on one or both armor pieces. Or if you find that you really need more fire resist, you can still swap back to Divine Veil anyway. Vog Cub Coat + Divine Veil is a popular setup.