Thome is definately a HOFer, but there is no chance he gets in first ballot. If for no other reason than dumb luck, Jim played during the steroid era, and that fact reduces the value of the 600 home runs.
In the first 100 years of the recognized existence of major-league baseball (starting in 1869), one player, Babe Ruth, reached 600 homers. In the following 33 seasons, from 1969 through 2001, only two others made it, Willie Mays and Hank Aaron – and after Aaron in 1971, there were none for 30 years.
So, three 600-homer players, all legends, in 133 years.
Since the start of the 2002 season? Five (including Thome).
Right or wrong, the cheaters in Thome's era have lessened his accomplishments. Good guys like Frank Thomas and Thome will get in, but will have to wait a year or two to do it.