All depends on who the blank wheels are made by.
If the blanks are manufacturered by the same distribution company as the major brand ones, then you are on to a safe bet, they are going to be the same, or only slightly less quality.
If they are the budget blanks you see about, then you can never be too sure. They never really offer much detail in the wheel hardness or material, so you take a chance on them.
In the bigger picture though, buying blank wheels means that no pro riders are being paid from your purchase. If you have a favourite skater and thinks he deserves lunch on you then you should probably buy their wheels out of gratitute. The industry depends on pro's being allowed to express skateboarding, spread it's message and add to it's progression.
But I don't think anyone would blame you for buying blanks, it is money after all and it does all add up!
8 years skateboarding