"although I dont recall a way of knowing (at least trailside) if the snake has or hasn't delivered any venom."
You really want to take a good course in backcountry first aid, because that is a topic that is taught. If you can accurately decide whether venom was delivered, it will help you decide the other things, like how much to rush the victim to the ER.
Start with the assumption that it was your basic, garden-variety, angry rattlesnake. Once you have verified that the snake is no longer a danger, you examine the wound site and look for two holes a fraction of an inch apart. If there is venom in there, it will likely develop swelling, redness, and soreness within five minutes. You can take that time to assess the situation. For other venomous snakes, it's different, so you need to be wise about the risks in your area.
Some venomous snake species cannot deliver a lethal dose no matter what they do to you, so a little training can go a long way.