There is a NATO/Ukraine
training center in Yavoriv, a few miles from the Polish border. Russia hit it with cruise missiles a couple weeks into the war. This
Buzzfeed article about the attack has a picture of Florida National Guard members training Ukrainian solders in early February. I imagine regular soldiers were all pulled in later in February, but there were US/UK/etc. "volunteers" onsite at the time of the attack. They turned down the arms Ukraine offered because they already had better ones "provided by a third party".
Even if these particular westerners at Yavoriv were truly volunteers I can't imagine we have zero personnel in country. Not just to train Ukrainians, but also to assess needs and gather intelligence.