I presume that when you speak of the adverb "блискo", you are in fact referring to "блиску". If so, I would tell you that there is no significant difference between the two, as far as I can tell. I don't even understand what the difference between "near" and "close (to)" would be in English - in both cases, it appears to me that proximity is being suggested and nothing more. Thus, both "близу до" and "блиску до" would work in the same way for me in all cases I can imagine.
As for "блиско", it is only a neuter adjective - I don't believe it can be used as an adverb like all other neuter adjectives.
Yes, sorry i meant блиску. I too don't really know the difference between "near" and "close to", the only thing that differentiates them to me, is the used of a preposition in "close to". Is it possible to say близу мене? Or does близу always require a preposition?