I don’t think so, but I’m not 100% certain. The quote that BB posted, “...while playing in a PGA Tour event...” doesn’t necessarily apply either. The US Open is not a PGA Tour event.
Yeah, but that is a USGA rule. Here is the waiver. It doesn't specify a PGA Tour event - I believe that was just an example by the author of the article.
PRIZE MONEY WAIVER FORM
Rule 3 (Prizes) of the Rules of Amateur Status prohibits an amateur golfer from playing for prize money
(i.e., cash) or its equivalent in a match, competition or exhibition.
However, an amateur golfer may play in a match, competition or exhibition offering prize money, as long as
he or she waives the right to prize money in advance. An amateur golfer may waive the right to prize
money by either 1) submitting an entry as an amateur golfer, or 2) informing the Committee that he or she
is waiving the right to a cash prize in advance of participating.
NOTE: If players are able to submit a competition entry as an amateur golfer, they are considered to
have waived the right to prize money by doing so.
The USGA makes this waiver form available to assist those amateur golfers who wish to protect their
amateur status by waiving the right to accept prize money. Amateur golfers who wish to do so should
submit this form to the USGA or the appropriate Committee, no later than the first day of the competition.
This form is also applicable to applicants for reinstatement who wish to play in an open competition and
waive the right to prize money.
By signing and returning this form, I hereby certify that I will not accept prize money.
Name of Competition ___________________________________________________________
Date(s) of Competition ___________________________________________________________
Name of Player (Print) ___________________________________________________________