Saison yeasts are typically pretty temperamental (French strains like 3711 are easier than the Belgians) but still, not overly surprising that it wasn't fully died out yet.
Don't worry though, if anything that fruit and the extra sugar just have the yeast a little kick. Don't worry about racking it off the cake, the yeast that had already settled out wasn't doing much anyway, there's still plenty in there to finish the job.
Be patient, if it's stalled and not fermenting further, move it somewhere a little warmer. You definitely don't have to resort to Brett, you could always add a little more fermentable sugar and/or another pack of 3711. But you shouldn't even be thinking about that for another 2 weeks...
My only problem with raspberries that early is that sometimes you can pull some tannins out of the seeds. I usually try to only let my beer sit on raspberries (or blackberries or strawberries) for a week, 2 at most.