How Inbox works with Gmail[ed - imho, it is not too bad. It captures some gmail Priority Mail features in a simpler way, like adding a "lower-priority" grouping that is easy to manipulate, it does more quickly display the attachments in the mail when that is the point of the mail, and it integrates some functionality I only got by adding Boomerang to gmail (delay the reading of a mail).
I still need Gmail with boomerang for the "send later" features that I use on the PC, as Inbox doesn't have that. On my wifi-only tablet I still like the gmail caching of some categories in priority inbox in gmail for offline use, I'll have to see if Inbox interoperates nicely there in offline mode or not. It does seem that Gmail and Inbox do interoperate smoothly as advertised when on wifi, so certainly it is possible to use both, especially on a PC. YMMV :-) ]
How Inbox works with Gmail - Inbox by Gmail Help