Not that I am aware of.
Specifically, I'm not sure how you would upload a KML to Google Maps app itself even when online. I usually have to go through My Maps, and for the best experience importing data I do it on a computer rather than a mobile device, save it in My Maps, and have access to it from Google Maps app from then on. I can do it from a mobile device but have to go through my browser, set it to desktop mode, and then have access to the right paths to import data files. Doing this on my phone is frustrating, on my 10 inch tablet it is tolerable but still cumbersome.
I'd love to know if someone finds a way, not just to import a .kml but also if there is a way to store My Maps offline. I searched some and it appears the feature is frequently requested, it may be implemented at some point, in the last few years Google has really improved their map interfaces, I'm using Google Maps for things I would have needed stand alone software for prior.
I did some testing, disabled WiFi and Mobile data, then attempted to access my data. It looks like it will remember and access cached data, a recent map I looked at loaded initially, but there does not seem to be a way to save My Maps data offline. I selected a map I have not accessed in a while and it would not open because it was hunting for data. I woulden't trust it even if cached though, as you never know when it will decide to toss that data.
Maybe we should all use the feedback feature to request the capability. The more people want it, the more likely they will add it.