A spectrum analyser will show you what is there but only with your ears can you tell what is noise and what is good signal, unless you have a very obvious bump like a hum or whistle.
A lot of the skill in reducing background noise elements is editing out noise and applying fill if it is a noise like background kids voices. Also selecting and cross mixing between the two mics will reduce background by just focusing on the correct channel. For these reasons, I would not blanket noise reduce the whole clip, but treat each on its merits.
Also just in case you do need to export an OMF for external audio work, your original clips should remain unprocessed.