In answer to your literal question, is 'real-time' understood - in the context of a drawing app - outside the tech community,
the answer seems to be a resounding yes ..
flockdraw.com ...
You can have unlimited people in a room and the drawing updates in
real time
twiddla.com ...
...in a shared, real-time whiteboard...
Colorillo..
colorillo - real-time action painting
drawitlive.com ...
Draw it Live is a free application that allows you to work together with other people to draw in real time...
google's 'Drawings' ...
... covered features like real time collaboration, online chat, and
Simply using google to look at the many real-time drawing apps (collaborate in real-time), I'm pretty sure the term is used, actually, for every such app.
I think you can definitively say you'd pretty much have to use the term; it seems to be the standard in the field. A few but not many also use "live" in their marketingspeak: for me, as others have expressed here, "live" means something different. And this seems to be the consensus as "real-time" is used seemingly universally and live is little-used.
I agree with the various concerns voiced here that "real-time" is not really a perfect term, for real-time drawing apps - but it does seem to be pretty much what can only be called the standard term. And that's in both the companies themselves using marketingspeak (and/or names), and writing (reviews, etc) about these products.