I did not think of this, but it's a good idea. Montagu/Montaigu are well-known names that may explain why this "Collineau de Montaguerre" is so popular. I have never found one with a serious source attached to it.
You are correct that "Montagu" should be preferred to "de Montagu" in the Last name at Birth, for members of a noble house anyway.
Not sure about those articles in other languages. In France you see the "de" coming on and off until the Revolution (when, understandably, "de" tends to disappear altogether, only to reappear - consistently, this time - after the Restoration) so I almost never include it. I understand the use of "von" in German, for instance, was consistent earlier on.