It's kind of like asking if Hollywood celebrities are reliable. My response would be, "which one"? :
Which meditation technique?
And whose mind is doing the meditating?
If, for instance you asked if George W Bush meditating on Guru Yoga with Miley Cyrus as the Guru was reliable: as in, per your question, would it produce recollection of his previous lives-- I woud say-, probably no! It would likely produce something else entirely
Man, I want to see a thangka of that.
But how do we know that we weren't "fooling ourselves" as it were? Reading the SecularBuddhistAssociations rejection of Rebirth, one of it's points is that we could potentially invent or falsify memories.
If you approach this from the viewpoint of scientific materialism..you will never get a satisfactory answer. If you take that viewpoint, agnosticism about it is the only sensible position. Current scientific materialism pretty much shares with Buddhism the idea that "life" generally is an illusion (the term from people like Daniel Denett is "manifest image" I believe), but it believes that ultimate reality (which for materialism, is of course only material - no explanation at all for consciousness other than that it somehow arises from physical matter) is only had by inference based on physics and empirical evidence..essentially. This means, that ultimate reality of things from that viewpoint can never actually be experienced by you, only inferred.
I.E. You cannot experience an atom for instance, there is no 'direct experience' of how things really are.
From a Buddhist standpoint this is a little crazy, because you are accepting the reality of a world you can never experience based on inference, but you refuse to accept the reality of something based on inference from your own experiences
So, you have to ask yourself what constitutes a valid experience, if you decide it is indeed possible to experience something like a memory of a pasty life as-is..then you have your answer. if you take the materialist point of view though, you are always relying on "proofs" which amount to something other than direct experience.
Hope that makes some sense..i'm not saying don't be skeptical, i'm just saying you need to examine want actually constitutes "proof" of something in this context.
One thing I will say, the more you meditate, and the clearer you can see your mindstream, the more outlandish the proposition of things being "invented" by your mind seems, there are some deep, deep patterns there.