Team workouts are important, but I would doubt if they'd even be the secondary piece of data in terms of making a decision. Fultz has been heavily scouted for years, and teams have sat in in practices as well as games. Making a decision based on a single day's workout, or lack thereof, is pretty short-sighted, barring him going Latrell Spreewell on a coach (which there's been no indication he'd ever do.)
As for his school choice -- Romar at Washington has consistently put less-heralded high school players into the NBA where they've gone into have at least some success. The most notable is of course IT, but others include Terrence Ross (#48 ranked recruit), Marqueese Chriss (#56 ranked recruit), Dejounte Murray (#46), CJ Wilcox (#108), Quincy Pondexter (#48), Brandon Roy (#36). All of those guys went on to become 1st round picks, despite none of them being even in the top 30 of their high school class. He only ever had two top-10 recruits (Martell Webster and Spencer Hawes) but they both went in the 1st round as well. He also got a few other guys from outside the top 50 into the 2nd round of the draft. Consider how many top-20 recruits Kentucky, Duke, and Kansas get that don't ever make the 1st round, and it's clear that Romar's failing was not in player development, and as such, we shouldn't worry at all about Fultz.
He was a terrible in-game coach. As a friend of mine who is a big UW fan told me: "If you want someone to turn your son into a man, you want Lorenzo Romar. If you want someone to make your son into a great basketball player, Romar can do that too. If you want someone to win basketball games, go find someone else. He'd miss the playoffs with the Warriors."