I haven't read up on RA myself, other than what I've read here, but are you saying that honesty is a basic tenet of RA?
I haven't done much further reading on RA, myself - I have too many other things to read! - but, based on what I've seen up to this point, I think it wouldn't be quite right to say honesty is a "basic tenet" or a "core value".
It's deeper than that.
If RA is about two individuals negotiating the terms of their own relationship without following any particular script made available by the society (e.g., romance, "the friend zone", etc.), then honesty strikes me as just one of the conditions on which negotiation - in any meaningful sense - is possible.
On that score, RA strikes me as beautifully optimistic: individuals can, without any sort of external social control or guidance, work out the terms of their own relationships . . . so long as the negotiation is done in good faith, on a basis of honesty, reciprocity and consent.
It's bottom-up social organization, one dyad at a time.
And, as I say, it's beautifully optimistic.