We absolutely do not do routine suctioning on any baby of any gestation. With a little micro, I only suction as a last resort (baby desatting and doesn't come up, bad gases, etc.). Too risky due to IVH, pulmonary hemmorhage, etc.
Our facility uses both HFJV and HFOV. And yes, with Jet vents, you absolutely should put the vent in standby mode (the baby still gets conventional support, just not high-freq), suction quick, and then turn back on. If you don't put it in standby mode when suctioning, the vent can sense that its not able to give the ordered amt of pressure and will try to compensate, thereby increasing your risk of pneumo. At least, that's my understanding of the Jet. They are pretty complex machines, but work great!