In general, I don't believe so. Your not exactly going back to a restore point, it's more like you can go back in time and bring an individual file back with you to the present. In most cases, this would be a document, photo, or similar file which would not be affected by an OS update. It's unlikely you would go back 6 months to extract a system file that is Leopard specific.

And in the event of a HD failure, you would most likely be restoring to the most recent backup, not one from a previous OS.