Most all current pro's use a variant of semi western (the thumb along the top horizontal face of the handle) as their standard grip. Hewitt in fact uses an "extreme" semi western, as against Henman and Agassi who use a milder version.
I don't think that anyone uses full western (thumb up the back vertical face). Berasategui used to.
Pro's do of course have the ability to change their grips from stroke to stroke - ie bit more western when playing from behind the baseline, to more eastern when stepping up to hit a flat winner.