Yes, the repair manual designates the cap with the oil pump screen as the
drain, but the other bolt is still a drain. What else could it be? Side note: You'll always get more oil drained by using that side cap. Don't over-torque the cap, many get destroyed when they get stuck.
A self-tapping bolt, is essentially a tap, with a hex head on it. The only way it would damage anything is over tightening it. Oil plugs, the cap with the oil pump screen, and bleeder valves, never need to be torqued tight, just snugged is enough. Even if the self-tapper strips out, a Time-Sert, or helicoil can still be done. Tapping threads for a larger bolt, is the same as using a self-tapper.
I've seen many rubber expansion plugs just pop out, with oil and coolant, and always at the worst time. I oiled a mile long stretch of highway once. Company mechs used a rubber expansion plug on a truck that holds 3 or 4 gallons of oil. Oil covered the lane I was in.
You can do a Time-Sert, or helicoil at home if you're mechanically inclined.
You can make your own self-tapper with a bolt and a hacksaw. But they're cheap to buy, and there are some with their own drain plug. A self-tap bushing gets threaded into the hole (loctite would be good), then a drain plug threads into the bushing. I've never had any trouble with self-tap plugs.
Self-tapper bushing and plug