When you say "Vajrasatva purification practice" do you mean an appropriate visualization plus the hundred-syllable mantra followed by a dissolution?
If so then the answer is: no, this is not training in the Ultimate Bodhicitta, this is a preliminary practice.
If by "Vajrasatva purification practice" you don't mean the above mentioned sadhana but instead you mean the cultivation of the view that "In the absolute sense there is nothing to be purified, no one purifying, and no act of purification" - then that's training in Ultimate Bodhicitta.
There's nothing to be purified etc, - means you no longer regard yourself as a problem. Things don't require fixing because nothing is broken. In the ultimate sense everything is exactly as it should have been. All judgments like "dirty" and "pure" are mind-made categories, defined relatively to one another. That's the view of Emptiness.
When you cultivate the view of Emptiness, you get used to the idea that to let go and to open up is okay. You stop being driven by your hopes and fears and come out as authentic being. Instead of pretending to be perfect, you figure things out as you go, and that creates a sense of kindness and openness. Now you can actually relate with people.
This is why they say, first cultivate the Ultimate Bodhicitta and only then the Relative Bodhicitta. Because the view of Emptiness is what gives that authenticity and relaxed attitude, that sense of not forcing your preexisting agenda on people that makes it possible to meet the real them. Only then saving others from samsara, the point of Relative Bodhicitta, is possible.