Honestly, yes it's probably possible. There are a lot of people who understand poker far better than I do who'd probably say it couldn't be done, but there is a very strict by-the-book right and wrong mentallity attatched to online poker. There is more than one sollution to seemingly obvious situations, we're just all trained/conditioned to think in similar ways (by "we" I'm taking a leap and counting myself amongst decent players).
With that being said, I stand by my comment that tricky and conservative players who limp are fish. The enormous vast majority of them are, such a high percentage that you may never come across a good player who does limp. The logic by which newer players decide to limp is usually along the same lines and demonstrates a lack of understanding of various factors which make it a horrible play. They aren't thinking about how balanced their range is (I'm not using "balanced range" as "unexploitable range" but rather "thought out and optimal") and they're often miscalculating the equity difference between limping and raising even before we bring game theory into the question. Noteably, they're forgetting about the blinds they're unable to steal and how transparent their hand is after taking various lines, even fish will likely be scared off by their value bets. Those who aren't so new to poker strategy
that they're going to make these common blunders, will not limp.
Simply put, yes, limping is a sign of a fish. If you frequently see limpers who are not complete fish to you, you need to sit down and do some studying because these players are exactly the guys who should be contributing a lot to your winrate.