If he was built more like a Mo Rivera, then not many concerns at all about his using but his head is as big as Barry Bonds was and is one of the signs associated with using roids. Lets just say if he is using, i and many others would not be surprised at all.
When Bonds started with the Pirates, Bonds was also a sleek, thin guy who could hit, but his limit was maybe high 20s, low 30s HR a year.
http://www.baseball-reference.com/players/b/bondsba01.shtml
In fact, Bonds HR production with the Pirates was (starting in 1986 to 1992) 16, 25, 24, 19, 33, 25, 34.
With the SF Giants, he hit (from 1993 to 2007) 34, 46, 37, 33, 40, 37, 34,
49, 73, 46, 45, 45, 5, 26, 28. Bonds was age 35 to 39 when he hit 49, 73, 46, 45 and 45 HR's.
David Ortiz's OPS was never over .839 when he was with Minnesota. The most HR's he hit was 20 when he played 125 games. He had 58 HR's in 6 years with Minnesota. He didn't play full seasons, but he was not a power hitter.
http://www.baseball-reference.com/players/o/ortizda01.shtml
His OPS exploded with Boston. The first year with Boston his OPS was .839 and then from there it was close to or over 1.000. Ortiz is 37 and he has an OPS of over 1.000 last year and this year. Ortiz has averaged 32 HR's a year with Boston in 11 years, with a low of 23 (last year) and a high of 54 (2006). At 37, he is on target of hitting 30 HR's if he stays healthy.
So is David Ortiz suspect of using steroids. We know that his teammate Manny Ramirez certainly did and both were the same size --- BIG, REALLY, BIG.