The app's about screen notes that "we do not use any API provided by Instagram to prevent possible blockage", so the assumption is the app is using a method it feels is not in violation of Instagram terms of service. As we have previouly noted Instagram is keen to protect its service experience and generally frowns on third party apps that attempt to emulate the Instagram experience.
#2InstaWithMassiveLove, API usage aside, is no different to any of the other third party Instgram apps in this respect, and it remains to be seen whether Instagram will take any action against the range of app thats have been poppping up on Windows Phone in the last few weeks.
Incidentally, despite the simlarity of the name with Nokia's promotional #2InstaWithLove app, #2InstaWithMassiveLove is most assuredly not an official Nokia app, rather it has been created by third party SmokedByWindows8.
Windows Phone Store description:
The fully featured third party Instagram client that allows you to upload UNLIMITED amount of photos to the social network!
Check out your Instagram feeds, like photos, comment, follow..
#2InstaWithMassiveLove, which support both Windows Phone 7.5 and Windows Phone 8, can be downloaded from the Windows Phone Store. The app costs £0.79 / $0.99 / €0.99. A free trial is available, which is fully functional, but ad supported.