I am very glad you liked Oakeshott. Your first impression conifrms my opinion that those who think Oakeshott was an archi-conservative would have changed thier opinion - if only they had read him!
I agree with you that Oakeshott, unlike Arendt, minimises the significance of the political. Yet this is precisely why I like him. It does not mean that he completely disregarded politics. Yet he thought that politics should be kept within strict limits, and that its significance should not be overstated. He considered politics to be 'a second-order activity', which is required in order to provide room for the things that are important for the civilisation (and which I call 'the green grass'), but which cannot be seen as possessing any inherent value.
The question of how all this is different from Arendt's position is a bit complicated. At first glance, the two thinkers seem to be poles apart from each other. Yet, it seems to me that Arendt, in her idiosyncratic ways, gives politics a meaning very different from the common one, and probably different from the one that Oakeshott attacks. In a certain sense, she seems to be incorporating politics into the realm of the green grass, whereas she sees in the 'social' the main danger to the green grass (although of course her green grass is not my green grass - it is too coloured by Jeiwsh neuroticism, but then, who could blame her?) - politics being bestowed with some element of aesthetic significance and clasicist nostalgia. And this is why, although Oakeshott is certainly different from her, they could share something in common not on the level of philosophical generalities but rather on the level of practical attitude to some social and cultural issues of the modern world.
I must confess that, being a down to earth historian of ideas I am, I always find it difficult to make sense of a too abstractly formulated philosophical discourse with its preoccupations with 'epistemology', 'ontology' and other clever words. So your second paragraph was a bit dense for me. Perhaps, we should have a long conversation on this on Friday, so that I will understand what you mean by speaking about the 'ontology that follows the demise of realist phenomenology to be replaced by existential phenomenology', in order to be able to feel with all striking intellectual clarity the sweetness of my ineivtable intellectual defeat at your hands.