Yeah, paying at less than the advertised wage is insulting. Unless they give you the 20% of the first three months back after the probationary period.
It's scummy.
You could simply hire better employees rather than disrespecting your candidates. I wouldn't bother pretending that it has anything to do with "risk management". At best, you sound extremely cheap. At worst, it makes you sound like you repeatedly make poor hiring decisions and scramble to adjust for this.