That little flowering plant is cute, I had a zkittles like that once. You'll be surprised by how much it spreads out by the end.
To my mind silicon dioxide is not going to harm the pollen, but I don't generally mix it into it, I use it for my seeds, to keep them dry once they've been stratified.
The silicon dioxide should help a plant, overall, especially to establish roots. But pollens? It's an unknown for me, but I would think it should be safe, if the ph range is correct. It should only be a weak acid, which I would think, should be fine.
Silicon dioxide has no basic properties - it doesn't contain oxide ions and it doesn't react with acids. Instead, it is very weakly acidic, reacting with strong bases. Silicon dioxide doesn't react with water, (it absorbs it) because of the difficulty of breaking up the giant covalent structure.
It could however, make the pollens too dry, but extracting every tiny bit of moisure of it. I would think there's probably a balance in there somewhere, and pollens contain around 10-20% moisture, when fresh, ideallly about 4% dried.
I would just keep the silica in it's container and store it with the pollen, not mix it together. If need be, wrap it in a tiny peice of coffee filter, then put them side by side, sealed, then freeze. But let the pollen dehydrate first, stratify. This is key. I'm pretty sure this will work, and others here probably have more experience than I on this subject.