My take is that if information, isk, gear, or anything else whatsoever passes between the two characters OOC, it passes between them IC. You can invent various ways to connect these two characters, same as you would two characters that belonged to different players - are they relatives or friends, is one doing a job for the other, being blackmailed, etc; there's loads of options.
You can (well, some people can) also play two characters completely separately, without using each others intel or resources, obviously. A lot of people have two or more "mains".
I am personally very iffy about letting people have these "disconnected alts" of active reds in Gradient, because I don't think most people are actually capable of keeping information separate like that. It's not unheard of, but I cannot say I like it too much.
(Despite there having been "gentlemanly agreements" between some specific RPer parties that they do not use alts to spy on each other, you should never assume any general rule about it exists - not the least because there cannot be a general RPer rule, but also because a lot of, if not most, RPers simply don't feel it is a problem outside of such explicit agreements.)