Could the planets in the Solar System have been captured? Ignoring any current beliefs, is it possible that the planets could have been captured by the Sun's gravitational force after drifting through space while retaining their axis of spin and speed?

Notably, Venus uniquely has retrograde rotation; how would this have come about based on current theories?
I'll address the second question first, Venus uniquely has retrograde rotation; how would this have come about based on current theories? The answer is that there are a number of hypotheses related to Venus's rotation. See the related question What is the current accepted theory as to why Venus has a slow retrograde rotation?. None of them involve capture of a rogue planet. Note that this also applies to Uranus; it too has an odd orientation.

So why not? Note that I am now addressing your first question, is it possible that the planets could have been captured by the Sun's gravitational force after drifting through space while retaining their axis of spin and speed?

The answer is simple. Capture is extremely unlikely (and that's putting it mildly), and it is not needed to explain the odd orientations of Venus and Uranus.