I am not sure what you are saying with respect to red lines.

Vietnamese government will not arrest a tourist foreigner for talking bad about the party or about Ho Chi Minh, it would decimate their tourist bottom line. If you don't deal with drugs or actively don't organise against the party, you will be fine.

There is a growing surveillance (which you cited well) but mostly for locals.

edit: oh I misread, you are Viet Kieu, not a western tourist. OK yeah that makes some sense.