Just trust me on this one.

Bodybuilders tend not to lie about their heights. Weights, yes. Heights, no. Although King Kamali claimed 5'9.5", and I don't think he was being truthful there. There are some other cases too.
Dexter is 5'6.5". Dorian is 5'10.5". Although with that said, we lose around 1cm per decade starting from age 40. So Dorian may be 5'10 by now, but I don't think that is the case. Ronnie Coleman more likely lost height. He was also 5'10.5", but with so many back [and neck?] surgeries at this point, I wouldn't be surprised if Ronnie lost a full inch in height. Hulk Hogan went from 6'8 to 6'3 for that reason.
Having been to 17 expos over the years, I can tell you that bodybuilders are generally honest about their heights. I am basing that on my height of 5'8.5", given that I wear bit of a chunky heal and have big hair, making me look more like 5'9.5". And my impression is that over 90% of bodybuilders tell the truth about their heights. Weights are another matter...