napa %a is set to 0 so while will not work. think
um yes you can use a while loop. this should do the same thing as ur\'s.

alias mass {
  if ($me isop #) && ($regex($1-,/^[+-][ovb]$/)) {
    var %a = $nick($chan,0), %o = 1
    while (%o <= %a) {
      var %m $addtok(%m,$nick($chan,%o),32), %m $remtok(%m,$me,32)
      inc %o
    }
    mode $chan $left($1,1) $+ $str($right($1,1),%o) %m
  }
}