Is it correct protocol to be able to split a bibliography into more than a single column? I've been informed by my peers that a bibliography must always be presented in a single column i.e. each item spans the width of the page - even if the main body of the document is presented in more than a single column. Is this correct?
It really depends on where you're publishing. Two-columns is mandated in some venues, in others one is. I suspect that there may be a few rare venues where there is no single style, but that your field usually uses one column. 

If you are writing a paper, then you should look at the style guide for the venue you are publishing in, if there are none (which would be surprising) try looking at past papers published at that venue. Many venues simply supply the latex class you should use and examples. If you are writing a book, then a single column is usual from what I have seen. If you do not have a venue in mind yet, then you can just use a single column and change it easily later.