I think it's prudent to acknowledge specifics. With the Theravāda & Sarvāstivāda śrāvakamārga, experience is reducible to momentary minds, mental factors, and forms, all of which are to be recognized as impermanent, unsatisfactory, and selfless. The purpose of these recognitions is to sequentially terminate the ten fetters and attain liberation.
With the dzogchen rang grol lam, experience is reducible to rigpa and the display of rigpa, which is to be recognized as alpha pure and spontaneously perfect. Thus whatever arises is naturally liberated without being established or recognized as "this" or "that" phenomenon, and there's nothing whatsoever to accept or reject.
What you describe is difference in theory, in explanation of what goes on. Insight into the three attributes is non-conceptual even in Theravada, and that is when they are the three doors of liberation. That's why I see little difference in practice.
From Mahasi Sayadaw's (quoting from him since he relies more on classical works than Ajahn Mun's lineage) "Fundamentals of Vipassana Meditation" (PDF
"But the present phenomenon is what comes up at the six doors right now. It has not yet been defiled. It is like an unsoiled piece of cloth or paper. If you are quick enough to meditate on it just as it comes up, it will not be defiled. You fail to note it and it get defiled. Once defiled, it cannot be undefiled. If you fail to note the mind-and matter as it rises, grasping intervenes."
"If you meditate, you find that what you see passes away, what you hear passes away. They pass away in no time at all. Once you see them as they really are, there is nothing to love, nothing to hate, nothing to cling to. If there is nothing to cling to, there can be no clinging or grasping."
"When one is well-practised in insight meditation, after the arising of life-continuum following the seeing process, insight consciousness that reviews “seeing” takes place. You must try to be able to thus meditate immediately. If you are able to do so, it appears in your intellect as though you were meditating on things as they are seen, as they just arise. This kind of meditation is termed in the Suttas as “meditation on the present.”"
"If you fail to meditate even at the apprehending, you get to form process and name process. Then graspings come in. If you meditate after the emergence of grasping, they will not disappear. That is why we instruct you to meditate immediately, before the concepts arise."
"You note it the moment it arises. You note it and it ends right there. Sometimes as wandering of the mind is about to arise. You note it and it quiets down."
"So, if you note the moment you see, hear, touch, or perceive, no subsequent consciousness will arise to bring about graspings.
“ ......... you will simply have the sight of the things seen, the sound of the things hears, the sense of the things sensed, and the idea of the thing cognized.”
As this extract from Mælukyaputta Sutta shows, the mere sight, the mere sound, the mere sense, the mere idea is there. Recall them and only the real nature you have understood will appear. No graspings. The meditator who meditates on what ever arises as it arises sees how everything arises and passes away, and it becomes clear to him how everything is impermanent, suffering, not self. He knows this for himself- not because a teacher has explained it to him. This only is the real knowledge."