It depends a lot on what you mean by 'vipassana'. A lot of Theravada teachers and branches have very different ideas of what that is. I think for most uses of 'vipassana' it represent a fairly different technique from Silent Illumination.
Vipassana tends to be analytical and Silent Illumination eschews analytical meditation as being too conceptual. When it's not quite analytical and focuses more on recognising the three marks of existence for insight, this is still conceptual from a Zen pov, because it employs signs and has an object of meditation.
There are some forms of Vipassana, such as taught in the Thai forest tradition, that are fairly similar to Silent Illumination. When I stayed at Wat Pah Nanachat, they told me that sometimes they would simply hand beginners with little previous experience with meditation a copy of "Zen mind, beginners Mind." It was more or less what they were doing, but it's not written in the terse and formulaic language as the pali suttas, which required a bit of work to get into.
But even so, though the method is similar in many ways, I think the embedded context is fairly different. What I mean by that is that in Theravada, you practise for cessation. This non-doing, awareness is meant to liberate you from affliction and eventually cease them, culminating in full enlightenment. In Silent Illumination, affliction and bodhi are considered non-dual and the focus is really more on enacting and integrating this nondual enlightenment than to liberate affliction. Hence in Zen, 'one enlightened thought makes you a Buddha, one deluded thought the equal of a sentient being'. But in equipoise there are no distinctions of affliction and enlightenment made, nor is it done with a view to attain something since that equipoise is itself manifesting buddhahood (ie, the old adage 'you are already there'). Of course there is some background expectation that one's afflictions will be liberated through this process (we practise, after all, to be free), but it's not emphasised to the extent that it is allowed to get in the way of the nondual view. The context is not quite the same and these differences in view make some difference to the method as well, imo.
That is more or less how I see it anyway. Others will no doubt offer other opinions. I hope this goes some way towards answering your question at least.
"Even if my body should be burnt to death in the fires of hell
I would endure it for myriad lifetimes
As your companion in practice"
--- Gandavyuha Sutra