It should be "haylos", one word. Standard modern Spanish is "los hay", but the enclitic pronoun with a main verb in initial position was normal up to the sixteenth century and survives in Galicia, which is where the famous saying comes from: "no creo en las meigas, pero haberlas, haylas" (there are several variant versions). "Haberlos, haylos" is fairly common, and clearly modelled on the Galician saying. I think it carries an implicit echo of it, and implies that whatever it is does exist, despite what you would have thought. That's why I've put "do" exist and "believe me". I thought about "make no mistake", which would be an alternative for "believe me".

I think you have to say "people like that" or "such people", rather than just they, otherwise it will seem to be referring to the "frutos", whereas actually it refers to "aquellos que están al acecho". "Such people", which is a bit more formal, could be used; it depends on the prevailing style.

I admit that "haberlos, haylos" is very concise, and it would be nice not to make the English too long, so maybe we should leave it as "people like that do exist", and cut the last bit. On the whole I'd include it, though, because it brings out the implicit emphasis of the expression as I see it.

--------------------------------------------------
Note added at 53 mins (2012-05-09 08:31:19 GMT)
--------------------------------------------------

Certainly you could say "there are such people" or "there are people like that", and these versions would be fine, I think. I've gone for "exist" because of the possible echo of the saying about witches, whether the question is whether they exist.

--------------------------------------------------
Note added at 1 hr (2012-05-09 08:45:57 GMT)
--------------------------------------------------

A different tack, which has just occurred to me: they're out there. You could extend it to they're out there all right, but perhaps the shorter the better. I quite like this, because it's about as short and snappy as you can get. It goes against what I was saying about the ambiguity of "they", but there could be ways round that; for example, you might say something like "reap the benefit" for "quedarse con los frutos", and then it will be clear that "they" refers to those that are "al acecho en la retama".

The attraction of "out there" is the echo of "the truth is out there", and the use of "out there" to refer to supernatural phenomena, which fits in well with the (possible) implicit echo of the saying about witches. More generally, it suggests something nasty and threatening, and the reference to "aquellos que están al acecho" is pretty negative.