He's not a lock. Marv was a total non-producer in the playoffs. He had only 2 TDs his entire post-season career, not what you want from a HOFer because: a) They should shine in the playoffs; b.) He played in a lot of postseason games; and, c) Manning at QB.
The regular season stats speak for themselves. The off-the-field stuff is a problem to the extent he was never an open book to the media, which differentiates him from many other guys with problems outside the lines. Marv also played in a small media market and won't have the media relationships to fall back on at voting time because of his reclusive nature.
I think Marv is 50/50 for the HOF. He's probably the best receiver of that class and, more generally, the best receiver of the post Jerry Rice generation. He real peers were Terrell Owens, who was often considered the best receiver of the 2000s, and Randy Moss. Marv was much better than either guy.
Marv's will be a widely discussed and debated nomination to the Hall.
50/50.