Certainly long hair sporrans are appropriate for civilian dress, in fact, for most of the 19th century, long hair sporrans, both goat and horsehair varieties, were nearly the only form of sporran worn, whether for day or evening attire. Today the long haired "sporran molach" is reserved mainly for evening dress.
It should be noted that Josh (Skye Highland Outfitters) has two distinct lines of hair sporrans. One is more along the traditional lines of military style, the other is for civilian attire, and is modeled after (or inspired by) many of the historical civilian portraits of Highland gentlemen. So while there are some hair sporran styles that would probably only be appropriate for evening dress, he has some that are more versatile and are meant to be appropriate for day wear. I've got one of these on order (Skye's roamer #2).

While long hair sporrans seem to certainly have fallen out of style in the past several decades, they are still more than appropriate. I'm thrilled to see so many people here interested in them, and I think Josh is kind of leading a trend or revolution back towards wearing hair sporrans for all occasions. Same thing with diced/Argyll hose. I think it's a move in the right direction for returning to snappy-looking Highland attire!