Can warforged become vampires? Send Tweet. #DnD
— The Quarantined Dungeon Master (@BigSquishyDM) February 14, 2020
Under 3.5 rules, warforged couldn't become vampires. Under 5E rules, they are humanoids and thus technically could. Personally I would say that they CANNOT become standard vampires, for reasons too long to go into in a tweet; I'd create a unique warforged expression of vampirism.
— Keith Baker (@HellcowKeith) February 14, 2020
I think that both lycanthropy and vampirism are curses, so I feel like if you can have cursed items you can also just apply curses to warforged
Again it’s RAW vs. RAI. The editors of 3.5 thought it out and made the right call. That said Eberron is a messed up place so, sure, weird ass metal people vampirism over there, but go through the mists or into FR? That garden variety vampire just breaks a tooth on those metal necks.
And do we care ? No.