I've done it in a pinch, but the trub was over the level of the spigot so I still took samples the same way, and still racked the beer. If your spigot is higher up than mine is, it would work.
The only thing I'd be super conscious about at this time of year is fruitflies. Once you open the spigot, you'll get some dried beer inside the spigot and if you have any fruitflies, they'll head right for that spot. Since fruitflies tend to carry aceterobacter (among other things) they are my greatest enemy in the summer. We have a garden and always have tomatoes and things in the house and seem to always get some fruitflies this time of year.