Wikd played a game earlier as fiora and laned against fiddlesticks and couldnt hold his own do to fiddles drain targeting her during her ult. Is this meant to happen or a bug that has to be fixed? If its meant to be, is fiddlesticks a plausible counter for fiora?
It will most likely not be fixed, as this is not a bug. Leash effects can hit untargetable champs as long as they stay with in range. Nocturne's Fear leash, Morgana's Ulti leash, and Fiddlesticks' Drain can all his champs like Fiora, Vlad, Fizz, and any champ using an Hourglass (though while using hourglass you can negate any negative effects that proc during the untargetable durration. Fiora and Vlad will get feared or stunned while in their Untargetable state.
I don't think anyone can tell you if this is a bug or not because we don't know what Riot intended.
I can confirm, however, that Fiddlesticks drain will continue to target and affect Vladimir even when he uses Sanguine Pool.
The drain sould start before the Fiora ult, and only way to interrupt drain is to go away its range or to wait until it ends.
This is not a bug.
Fiddles ult along with morgana's ultimate also maintains contact on champions even when they become untargetable. Another notable example is vladimir pooling, in which he can still be stunned by morg ult, drained, or killed by ignite. The same is true for fiora.
This is a bug where fiddlesticks can ultimate people while they are using their ultimate or if they are out of line of sight such as up the cliff above him.
It probably won't be fixed as it isn't game breaking.