In book II, Ar. describes ethical virtue as relating to/being encompassed by pleasure and pain. Wouldn't this make him ascribe to a Hedonistic worldview, and likewise commit him to believing that pleasure could be pursued for its own sake?
First off, let's split your claim into two parts. The claim that Aristotle says "ethical virtue ... [is] encompassed by pleasure and pain" or something to that effect is utterly and completely false.
The the part that says "Aristotle describes ethical virtue as relating to pleasure and pain" is true and comes from Book I and again in Book II of the Nicomachean Ethics.
But we need to be very careful in understanding how they relate for Aristotle.
First off, let's give a basic definition of hedonism. I will take hedonism here to mean that the goal of life is pleasure and the good is to have as much pleasure as possible.
On this definition, Aristotle is not a hedonist.
For Aristotle, pleasure accompanies being ethically good for the phronemos (the man of practical wisdom). For the rest of us, we can have these signals go terribly wrong (this is all in Book II of the Nicomachean Ethics). Pleasure is then a symptom of being ethical for the right kind of person.
As an analogy, we go to the doctor when we have things like fevers or coughs, but the doctor diagnoses the problem that is really ailing us. Generally, a fever is the body fighting off an infection and a cough is a response to something like phlegm collecting in the lungs. For Aristotle, the person who is practicing excellence (virtue) will get pleasure out of this excellence. But a person who is not virtuous will (sometimes) get pleasure from things that a truly virtuous person who find unpleasant. The same occurs in reverse for pain. In other words, pleasure/pain are not good signals for Aristotle.
Returning to the hedonism question, for Aristotle, the goal is excellence in performing the human function (Books I-VIII) or excellence in theoria (Books IX-X). That pleasure accompanies this is that the human function is what we are meant to do. But upbringing and other things that can skew our ability to perceive this signals.
hedonism = the good is pleasure and its pursuit.
Aristotle = the good is excellence and its pursuit, and if you do it right you will also get happiness and pleasure.
A second argument could also be offered by looking at how Aristotle considers friendship in BK VIII. There he divides friendship into three categories:
- Friends of utility
- Friends of pleasure
- Friends of virtue
The first two categories are temporal and inadequate and Aristotle does not think they are true forms of friendship.
J.L. Ackrill, Aristotle: the Philosopher
Amélie Oksenberg Rorty ed. Essays on Aristotle's Ethics, University of California Press, 1980. (especially the articles by Nagel, Irwin, Akrill, Annas)