Some commentators have argued that the Song of Solomon is a series of unconnected love poems put together by a redactor. However, the same themes/names/metaphors/phrases recur again and again throughout the book. For instance, agricultural and farming metaphors, the name Solomon, and the phrase "do not awaken love until it pleases" occur several places throughout the book. But is this sufficient evidence to discount the possibility of the Song of Solomon being a series of 5-12 unconnected love poems?
Your question poses an either/or choice where there are, in fact, many intermediate possibilities.
An editor could have taken a collection of love poems and edited them, with allegorical or other intent. The editing could easily have introduced the linking themes.
A single author might have intended a poetic conceit in a cycle of love poems. The idea of Solomon could be part of the conceit.
The poems could all come from a common poetic genre of the place and time. Such genres, in an oral culture, would lead to many common elements. Originality was not necessarily a virtue. Certainly all the agricultural/pastoral metaphors are just standard-issue -- now, if someone was compared to a locomotive, then us textural critics would be in a pickle.
I believe that a survey of the scholarly literature will find you all of these, not to mention the traditional 'G-d wrote it' allegorical views.
There is absolutely no support for this theory. Song of Songs is a fully developed allegory for a relationship between God and the people of Israel with a fully developed plot. If you take a piece out, the rest would not make sense.