Hey man a very interasting hail team you have here!
Looking at you teams threat list you mentioned Slowbro, Terrakion and Infernape as threats. Scizor can also prove to be a little bit threatining to your team due to it being able to beat Abomasnow and Kyuerem as well as Salamence and Gengar if they have taken a bit of proir damage with Bullet Punch. You mentioned Gengat to be your Spin Blocker but i think your team would have much more succes with Jellicent>Gengar Jellicent helps against alot of these pokemon being able to beat Infernape and Terrakion with Scald (although Grass Knot Infernapes can be annoying). He can also take on Scizor with Scald and Toxic Slowbro. Jellicent also fufills the same role as Gengar being a more reliable Spin Blocker defensivly. You miss out on a bit of offensive pressure without Gengar but you already have Kyuerem, Salamence and even Abomasnow who can do big damage. You may be skeptical in having two Water-Types in your team but with three resists to gras and 3 resists to electric that isn't an issue at all.
My only other suggestion is regarding your Rotom-W. With this being a hail team you already have enough Ice-Type coverage as it is weilding Ice-Type moves on 3 of your pokemon. A much better option for Rotom-W would be Pain Split>Hidden Power [Ice] especially with hail damage cancelling Leftovers Rotom-W will find itself getting worn down to quickly. Pain Split is a good way for Rotom-W to recover precious Hp points from your opponent. If you don't like the idea of using Pain Split then you can use Chestorest>Current Set which means swapping Leftovers for a Chesto Berry and Hidden Power [Ice] for Rest. This also makes Rotom-W a one time status absorber and is prefered if you don't find much options to use Pain Split on the opponent due to hail damage wearing them down to much. I highly reccomend trying both of them out.
Good luck i hope i helped!