With the weather as we are currently experiencing, the answer is a resounding YES! But to be fair, the long 'Indian Summer' of Oct & Nov 2015 has been exceptional, even this far south, in the Ariege. And also it depends on your interests; swimming lakes are a bit chilly at this time of the year, although sitting on a sheltered lakeside 'beach' is still very warm & pleasant. For skiers the opening of pistes must still seem a long way off but in reality the Ariege slopes will, in all likelihood, be open in a few short weeks, by mid-December. That is the unpredictability of the Pyrenees. Indeed, we had the first high snows yesterday. It can snow in any month on the highest peaks.
The Pyrenees winters tend to be short but cold in Jan & Feb. There has been a lot of snow in each of the last 3 winters with skiing continuing into Apr. Spring can emerge from mid-Feb; temperatures of 20+ are not uncommon in Mar. Summers are long & hot, generally mid-30 degrees. But the problem there in lies that the mountains generate storms mid-afternoon on most summer days. With so much snow accumulating each winter, the high mountain passes & paths are closed well into June and crossing the Pyrenees safely without the hindrance of old, compact snow is not possible much before the end of July. High-level snow, as mentioned, usually returns by mid-Oct. So, if you are seeking the heights, above 2000m, to climb and walk in warmth but not extreme heat, then Sep through until early Nov is a wonderful period to visit. For those not necessarily seeking the higher altitudes, but tranquility, a bit of history & culture, some fine cuisine and a warm sun on your back then, yes the Ariege is at its' very best in the Autumn! That said, there are strong arguments in favour of each of the Seasons. I will make those other arguments undoubtedly as time passes!