As the reigning Lillith player at my store I feel compelled to input on this. Personally I find that it is competitive but certainly more often than not feasible to beat the dreamer.
Most people seem to think Lilith is a veritable beatstick whose basic premise revolves around the alpha strike... while this works against a number of masters it is not her true strength. Lilith's strategy revolves around board control, and not the type like the dreamer has. While the dreamer can essentially "read and react" to anything thrown his way, Lilith and her crew use their insane speed to position themselves to either draw the charge and still be able to pull off the counter-charge or bring multiple charges to bear at once. Against the dreamer these are both very useful as in the first case you catch the rat out of it's hole so to speak (which as it's been said, once they're un-buried, the dreamer's minions are relatively weak), and in the second you force him/her to either split his forces or (more often than not) overpursue on the most valuable target leaving you open to bring the guns to bear so to speak.
This is one of the reasons I prefer the pure nephilim to the lelu/lillitu combo overall. Lelu is a hammer and lillitu is very tricky to work with, but the mobility of the hammer is far too low to even compete with the dreamer's speed, and lillitu is not going to be very useful against buried models and such. With a 5/8 for tots upto a 6/10 for a mature, you maintain the speed that you'll need to maintain the board control style lilith is best at, not to mention all the terrain nullifying effects and los-ignoring abilities.
With all that said there's two things I need to mention. First is as Lilith, you win and lose by initiative. I don't simply mean the flip to start the turn, but overall. If you get charged before you're in position, or get a vital model killed before you need it, you will lose. Once you lose the upper hand with Lil against the better crews (Dreamer, Zoraida, Colette, Seamus, Kirai, Teena, etc.), you won't be getting it back... and at that point you start praying.
Second is that this information is from mostly personal experience, which can be skewed by my local meta. While I preach all this, I have been told to have "ungodly" board control skills so for everyone out there don't expect to pick up Lil, use a few tricks to move some stuff around, and beat anything you play. You need to know your movement ranges, what can and can't cut what off, where you need to go, where your opponent needs to go, how fast he can get there, how he can get there, etc. for a start. People say Lil is the most straightforward neverborn master if not in the game. While she has very few "tricks" she's far from straightforward. Indeed she is probably the most difficult to truly master on that next level, since playing to her inner strengths is essentially playing a game of chess. One wrong move against an excellent player and you have nowhere to go, but make no mistakes (and avoid 3 straight black jokers...) and you'll win 95% of the time (even against the Dreamer).
PS: I don't get the horrible talk about the dreamer... he's fairly easy. It's Zoraida that's a pain in the ^%ing ass...