I have 3 gengar (1 caught as such) dont really like the squishyness or the power moves available, so no I dont think it matters, only things gengar would be super effective against are super effective against it.. and stupidly bulky.
the best movesets are usually
1. same type as the pokemon
2. charge attack is higher damage (usually the single bar, but Psychic and Bug buzz are the best for those types and is split into 2)
dragonites, how easy is it for you to get a decent rock type? Golem with stone edge is good,
seadra and cloyster (Blizzard) IF you can dodge that is, however seadra doesnt get STAB.
oh and dewgong gets also Blizzard, IF you can find a seel (2 more candies for my next try at Blizzard Dewgong)
fairies..... Clefable gets Moonblast.. Wigglytuff gets Dazzling gleam... BUT hyperbeam is better (and stabbed)as well as bonkers HP
oh and tentacruel apparently gets Blizzard as well.
just used my Scyther for the first time as well... its amazing (not on dragonites.. obviously)
Dragonites here have reduced in number.. due to being in a high water type area, dratinis do spawn as a result... but as horsea, shellder and Seel pop up with enough frequency they are cut down... and we had a Geodude nest for a time as well... meaning stone edge golems.
and due to water biome... we also go Gyarados (dragon pulse), those fill up the gyms around here along with vaporeon...
Vaporeon is just too important for me, even more then having Parasect is to nuke them into next week... along with slowbros... Gyarados... Lapras.... or anything else it fancies using Solarbeam on.
its a shame that Ice Punch (Poliwrath, Jynx) is rubbish as well. as both of those are easyish to get... got a few decent jynx, and 3 poliwrath (poliwag fairly common)
and all this talk of Gyarados which is annoying.. I now have a proper counter... 1301 CP Electabuzz with Thunder spawned next to my house :D
my 1505 cp Electabuzz only has Thunder Bolt (and Low Kick..)
1301 makes it handy for gym leveling as well.