Welcome to smogon! ÜI can really see this guy becoming one the best Spinners and Anti Spinners of the OU honestly.
Ability: Steelworker
Nature: Relaxed (0 Speed IV)
EVs: 252 HP + 196 Def + 60 SpDef
Item: Assault Vest
Moves: Gyro Ball + Earthquake + Giga Drain + Rapid Spin
252+ Atk Life Orb Excadrill Iron Head vs. 252 HP / 196+ Def Dhelmise: 144-172 (41.8 - 50%) -- 0.4% chance to 2HKO
0 Atk Dhelmise Earthquake vs. 0 HP / 4 Def Excadrill: 272-322 (75.3 - 89.1%) -- guaranteed 2HKO
252 SpA Life Orb Starmie Ice Beam vs. 252 HP / 60 SpD Assault Vest Dhelmise: 146-174 (42.4 - 50.5%) -- 1.6% chance to 2HKO
0 SpA Dhelmise Giga Drain vs. 0 HP / 4 SpD Starmie: 164-194 (63.3 - 74.9%) -- guaranteed 2HKO
And I'm not even talking about the other Spinners such as Kabutops, Donphan, Tentacruel, Hitmontop, ...
Gengar's nerf also helps him a lot when it comes to Rapid Spinning, now being able to go for the OHKO EQ on the switch.
Your EV spread is interesting, but if you could elaborate on it and explain what it does (beating spinners, perhaps?), it'd be great. Assault Vest will probably be its main item as it makes Dhelmise a competant bulky spinner AND spinblocker. However, despite Gyro Ball being generally effective on a slowmon such as Dhelmise, Anchor Shot should be the Steel-type (pseudo) STAB-to-go in all scenarios ue to its invaluable trapping effect. Giga Drain, even though it gets STAB too, is coming from an uninvested base 86 SpA, which is pretty weak. Power Whip is its best Grass-type STAB move and should be used if a Grass-type move is needed (for example, with your EV spread, Power Whip easily OHKOes bulky Starmie while also 2HKOing Excadrill). Also, why would you want to hit Gengar on the switch (and why would Gengar hard-switch into Dhelmise in the first place?) with Earthquake when you could hit it with a STAB Shadow Claw/Phantom Force?
Aside from that, I think Dhelmise would make a neat little addition to the OU metagame (or maybe UU, we'll have to wait and see how it unfolds) where hazard clearers (let alone spinblockers) are in great demand.