But if the wheel itself is hub centric, them maybe it's safe.
X1/9 Hubs are 58mm and huncenric wheels are 58.1 mm. I had custom adapters made to go on new hubs and at 58m, they simply will not go on. At 58.1 they are a very snug fit. I found this out by sending a new hub to the guy who made them.
If you have a hub centric wheel, the clamping force of the bolts with wobble bolts may be enough, and probably is, but I would carry a torque wrench with me and check it often during the the first few weeks just to make sure.
If the wheel isn't hubcentric, I personally would not risk it. And if the offest is not greater than 15 mm adpators would set the wheel way outside the fender. 155 mm is the minimum thickness that I've see available for adpaters.
There may be one remaing option to redrilling and tapping. If the wheel's center bore is greater than 60mm or so, I am sure someone could fabricate centering rings that would press on the hub and fit snugly in the wheel, thus making it a hubcentric fit.
Hope that helps give you an idea of what the pros' and cons are.