In two separate seeds I have found three nether fortresses that do not have nether wart.  One had no lava room and no interior rooms (just exterior paths).  The other two had lava rooms but only a partial and very small interior (one hallway) with no other features like stairs or nether wart.  It could be a coincidence, but it seems like a bug.

Seeds of games

-1250326861 (two found fortresses - one just paths and one dead end lava room)

409945588 (one found fortress with just a short interior hallway off the lava room)

Update - I did some more hunting in the second seed, found a second fortress, and also found nether wart.  I apparently just had a string of bad luck.  Sorry.  This can be closed.