If he has
to take one of the new stronger drugs (Enbrel, Humira, Remicade, Orencia, Rituxan) you could freeze sperm and bank it. Just in case. That's what Lance Armstrong did before he started chemo for his cancer.
Methotrexate shouldn't permanently effect male fertility but birth defects are possible so he'd have to be off MTX for 3-4 months before trying to get pregnant.
Sulfasalazine has definitely been shown to reduce male fertility - so stay away from that one.
Keep in mind that chronic high inflammation in the body can cause infertility too, so it is important to get the RA under control and the inflammation down. It can also cause heart disease, people with uncontrolled RA are at a much higher risk.
The PI sheet for tetracycline says it's contraindicated in women because it can have a negative effect on the baby but has no impact on fertility. They tested in male and female mice, 25x the human dose, and it didn't stop the music.
The risk of Plaq on a fetus is low but they don't recommend women remain on Plaq while pregnant or while breast feeding. Studies on male/female fertility are slim to none. There seems to be more discussion about Plaq in the Lupus community than in RA circles.