1.No, bullets are not (should not be) visible. Bullet should travel at hypersonic (>2 km/s) speed, which is barely reached even in artillery systems, to produce visible glow.
2.No. Generally, bullets are not visible even at night (as opposed to muzzle flashes). This is not quite convenient when shooting at large distances, as shells may be deflected by wind or the sights may be damaged. That's why every N-th (e.g. 5-th) round in the chain is a tracer. For Su-27 this is like: 1 tracer, 4 incendiaries, 1 tracer, 4 armor-piercing, 1 tracer...
Personal weapons (except machineguns) are usually not fitted with tracers - because when shooting single rounds, there's no sense in 1/5th of it being tracers.