from what I understand of the tendrils they don't touch physical objects until they become made of matter themselves - or become corporeal - so Oakla would only able to view them when they shift into corporeality where they have a physical form, thought it would be invisible to others, with her vision, since they are at that point in existence and made of matter she could see them
as for the Zha's fire, I never decided whether she could see astral matter, or basically space itself, however Shihaitans (including Oakla) can see distortions in the fabric of space, which is what she would likely see here, so she wouldn't see the fire itself, but rather the effect on space that it has - I imagine she would have to stress to see it as well, something like identifying a slight ripple in water.
On a similar note of seeing the effects of things, she can technically locate fire by watching the oxygen it has to use up to survive, but again it would require a lot more focus than a human's eyesight would just to see the light.
I hope that answers the questions, feel free to ask for a clarification if there's something that was a bit vague in the explanation
