Originally Posted by miscreant
No, macros can't check for CD's, but I'm fairly certain it's off the GCD, so you could just separate it from the rest.
/castsequence reset=target Hand of Gul'dan, Corruption, Dark Soul: Knowledge, Hand of Gul'dan, Metamorphosis, Doom, Doom, Grimoire: Felguard, Felstorm
/use Gloves of the Horned Nightmare
That should do what you're looking for. It'll try to use the Gloves every time you press the macro, so "/run UIErrorsFrame:Clear()" should prevent you from getting that red text spamming your screen while using this.