My city regulates fences to be no more than 6' in height. In many cases, the fence as a support for growing tall hedges that could exceed this height. I can't find a definition of a fence in my city codes - is it reasonable take the common definition of what a fence is and assume that a hedge won't be considered a fence for the purposes of height limitation?
It seems reasonable, but it may not be safe. If your city treats such fence-line hedges as part of the fence, and subject to the height restriction, whether under some provision of the city code that you did not find, or under a practice interpreting the code, they might enforcdce the hight limit on you. I don't know what this might involve: A fine, or a requirement that you remove the fence, or just cut it down to size, or what.
If I were in that position, I would try to ask the city - the city clerk, the public works department, or whoever is in charge of enforcing the height restriction. If possible, gent an answer in writing, or a pointer to a relevant city code section. That should be more definitive then anything we can provide on this site.