The show doesn't seem to answer this directly.
But I think it's still a great question.
According to an article on Rotten Tomatoes there are a few points to be made here:
- You have to sign a release form
- The hosts are also lifeguards
[Creator Jonathan] Nolan says he imagined clients signing a very comprehensive release form before being admitted to Westworld.
"I think the release that you would sign when you came to this place would be pretty extensive, would cover a fair amount of injury and risk involved in going to Westworld."
This tells us that there is a risk of injury when visiting Westworld.
2. Lifeguards and safety
In season 1, episode 5 we see the Man in Black threaten Ford with a knife. One of the hosts defends Ford ferociously but also does not counter-threaten the Man in Black. This suggests that that hosts will not only defend Ford - which makes sense - he is the creator and a company executive - but I think this behaviour somewhat extends to the guests.
The hosts are supposed to threaten and antagonise the guests in order to provide a thrill and a sense of danger but they generally do not go out of their way to put the guests in danger of serious harm. We see the hosts capture, punch and wrestle the guests but they do not attack them with things like knives or swords.
They are fine with using the park's guns because the hosts have been programmed to know that the bullets are not fatal to guests.
All of this is a theme of the hosts to appear menacing while secretly keeping all of the guests safe.
In season 1, episode 7 we see a guest and his hosts attacked by other hosts playing as native Indians. Despite arrows being loosed from bows, I don't think there was any actual danger.
You might think that the arrows don't have any built-in safety mechanism like the simunition (although we can't rule that out as a possibility) but they might not need to. I got the impression that the arrows were being shot at the other hosts and not directly at the guest. The guest wasn't riding very close to his hosts.
This isn't too difficult to imagine - as machines, the hosts would have a huge amount of dexterity, accuracy and knowledge of physics. As long as they deem their shot to be relatively safe then they can be sure they will not risk hitting a human with an arrow. Their calculations can be made in split-seconds and simply aborted if a guest could possibly be hit.
The narratives always play out so that the guests will not come to serious harm. I think of the Man in Black being able to escape after being tied up with Teddy - he conveniently escapes at just the right moment. The hosts allowed this to happen. (just my speculation)
3. Harm from other guests?
One question that often comes up is "what if a guest attacked another guest with a non-firearm weapon?"
I think the simple answer is: they probably can but it's against the law and/or park rules.
It's like if I go to a paintball game but instead of using the gun provided, I attacked the other players with knives, sticks or other weapons. This sort of thing might be in the release form.
We also notice that the hosts are quite pestering when it comes to interacting with guests. That is, they always want to be involved with the guests and follow them. This might be part of their lifeguard duties - to monitor and intervene if any guest-vs-guest fights break out.