As with most everything associated with helicopter flying, there is no simple answer to the question: Are downwind landings safe? There are just too many variables to make blanket statements.
But what are we really asking? Are we merely looking for reasons to justify landing downwind rather than exploring options that might take more technique?
Remember a couple of things:
1) A downwind approach could very easily mean a downwind autorotation if the engine picks that time to quit. Is that a big risk? Me, I haven't practiced any "for real" touchdown autos from inside the H-V curve. Your mileage may vary.
2) A downwind approach will certainly require more power to stop at the bottom, and there will be the real possibility that there won't be enough power, which will then require a run-on landing. The amount of risk here is dependant on how heavy you are, how high the wind speed is, and how big, flat and level the LZ is. Is there room to run it on? Can you run it on without rolling it over?
Let's look first at off-airport site landings. If I arrive at a site landing and find that all into-the-wind or crosswind approaches are blocked by a ring of orphanages, churches hearing Mass, chicken coops with irate, hat-wielding farmers and thatched-roof circumcision clinics, leaving my ONLY selection as a directly-downwind approach, I might decide that I don't really need to be landing there that day. If there was some urgency the compelled me to land, I'd consider the above risks very carefully. Then I'd follow the procedures outlined in that Transport Canada article, which is very good.
But philosophically, I'd weigh the risk of landing downwind with the risk of a very steep into-the-wind (or crosswind) approach, if one was indeed possible at all. Few site landings are so bad that you absolutely, positively cannot get in from some other azimuth than straight downwind. And of course helicopters have infinitely variable approach speeds, paths and angles. I'd use me noggin' and try to come up with an alternative. There is usually more than one single way to make an approach. I'd explore all possibilities before settling on "directly downwind."
The good news is that if you have a site that only allows a downwind landing, that'll usually mean that your take-off will be into the wind. That's good.
Finally, recognize that when you're making a downwind landing to an off-airport site, there'll come a time when a go-around is impossible. And that time might be pretty high up the approach. Once you fall back below ETL you are HOGE at high power. Sure, you might have enough excess power to initiate a go-around, but you'll surely lose altitude as you try to regain forward ETL, and your downwind angle of climb will not be impressive. How tall are those obstacles around your LZ?
So much for off-airport. What happens if you arrive at an airport and the Tower guy directs you to land downwind? Well, controllers do forget or sometimes neglect that we helicopters need to land into the wind just like the planks. Remember, our radios are transceivers. We can talk back to them, too. A gentle reminder might do the trick. "Umm, say there old bean, doing it that way will put me directly downwind. Might we come up with something else?" In my experience, this will elicit a response of "Do whatever you need to do, just remain clear of..." whatever.
No controller will force you to land downwind (unless the winds are really, really light). Even so, landing downwind to a taxiway is usually no big deal (let's just not make a habit of it). Oh, and don't expect me to always be able to do that to a small, congested non-movement area.
This of course presumes that prior to entering the traffic pattern you have visualised the airport layout, the buildings, the wind and where the Tower will likely have you land. If you have not done this, then you have not done your flight-planning properly. Remember, it's NOT GOOD ENOUGH to show up at the field boundary and be told to do something unwise, and then do it simply because you "didn't have time" to come up with another plan.
Helicopter pilots must be masters of improvisation. We make it up as we go along. Plan all you want, but there's always something that comes along to mess with you. So you have to be ready.
Any other simple questions?