The easy answer would be "no, because it isn't ex cathedra."
The correct one would be it is de facto.
The correct one would be it is de facto.
Infallibility does not depend on an ex cathedra pronouncement. This is an urban legend spread by the dissenters to cover their dissent on everything except the most formal pronouncements. What makes a statement irreformable or infallible is the definiteness and clarity and invocation of authority with which it is proclaimed. The pope has to make clear that he intends to settle controversy once and for all, has to make a clear, definite statement of the doctrine or dogma he wishes to define infallibly etc. You'll see that explained in the commentaries on Ordinatio Sacerdotalis whose URLs I posted in # 30.
Moreover, as the case of Ordinatio Sacerdotalis shows, even absent a formal pronouncement of the above sort, unbroken tradition combined with clear dominical institution already de facto makes something irreformable. So JPII in OS was simply affirming that the non-ordination of women was already an irreformable, infallibly taught doctrine and he could not change it (irreformable, get it?) even if he wanted to. Even doctrines taught in this way, in an overwhelming, ancient, unbroken tradition by the "ordinary magisterium" can be irreformable and infallible. Only when someone challenges them (no one challenged the non-ordination of women until 1976, when the Anglicans, who supposedly have valid sacraments--in their eyes--started ordaining what they claimed were true priestesses) does a formal statement with requisite definiteness, clarity, invocation of authority get made ("extraordinary magisterium"). That doesn't mean the doctrine wasn't infallibly/irreformably taught before the the extraordinary statement is made. And JPII insisted that OS was not an exercise of the extraordinary magisterium, rather, a confirmation of an existing ordinary magisterium infallible and irreformable teaching.
Personally, I think he chose not to use the extraordinary, ex cathedra statement in this instance because there was no need for it and using it is one of the things that Eastern Orthodox object to on the part of post-Vatican I popes. By confirming an existing infallible teaching, he confirmed what the Orthodox already believe, and did so on the same basis as they hold it to be irreformable. Had he employed ex cathedra extraordinary magisterium language it still would not have silenced the die-hard dissenters in the West and it would have unnecessarily alienated the Orthodox. To me it looked like he was trying hard to exercise his jurisdiction in a way acceptable to the Orthodox, which is what he called for in Ut unum sint in 1995.