I agree fully. I've seen several O8 players in PLO games playing what look to me like pretty junky hands with lots of low cards--like A237 or something with suited A. A lot of these wheel-like hands are not very good in PLO.
I'd never really thought about the conclusion you draw from this, though--namely, that a larger range of draws become scary in PLO. But it makes sense.
The main way I deal with it is pretty simple: Betting my strong draws exactly as I would sets. I feel like that forces them to "have it" when a scare-card hits because I may well have it myself.
Secondly, if they act like they're drawing and I have a set, I usually consider only the main draws as true scare-cards. Say the board is K75r, and I have KK. I'll probably continue to bet on any card except a 4 or a 9. 68 is the main component of any logical draw, so I view the cards that complete that particular straight as pretty much the end of my hand unless they let me draw for cheap to fill up. Anyhow, I don't assume that they necessarily have 4689 or 689T or something in order to make the call.
On the same board but with flush draw as well, I'm quite willing to check-fold the turn if the flush card hits or any 4 or 9, but I'll usually continue to bet otherwise (and bear in mind that I bet the flop, too, myself on 4689 or 689T with flush draw).
There, too, against players who will try to take it away from you on a check, I've had pretty good luck with being a bit tricky on my own flushes--like checking if I make it on the turn (or river) with a hand like A689 with suited A. Also, I think you're usually in decent shape if you check-call with some smaller flushes on a board like that. Again, since their straight draw is usually going to include 68 and becomes stronger with other middle cards, a T- or 9-high flush is often good after you've bet the flop and gotten a caller. A 6-high flush isn't and has value only in that it may block your opponent's flush draw (and gives you more clean straight outs). Hence, if you have maybe 4689 suited to the 9, and the flush hits the turn, then that's also often worth a check-call, whereas if you're suited to the 6 and the flush hits, you're better off check-folding.
So, basically, yes, you have to be worried about any draw completing, but my solution has been to try to turn the tables on them and make THEM have to worry about any draw completing, too.