I have used softwoods without issue. The longest I have had a piece in was maybe 1 year though. It didn't look different cosmetically but it was way softer than when I put it in and wouldn't easily be reusable if I was moving it around as it would likely break up into smaller pieces.
I don't really hunt for driftwood, but I don't hesitate to use something I find on a hike. Like many, I only take dead pieces of wood, I normally will be in Berkeley and don't want to upset the Hippies, among other reasons. I boil all my wood, no matter if it's from the wild or store bought. I just don't like a ton of tannins in my tank, or waiting for wood to sink. Boiling make any bark really easy to get off as well.