I hear a lot of mums say that babies waking through the night is a SIDS preventative. Is this true?

Waking a baby at night is not a part of any Safe Sleeping recommendations to prevent SIDS.
Maybe others are getting confused with research that has found that there is a link to babies who have died & the ability to rouse from sleep when faced with “a stress”
It is still Internationally accepted that Safe Sleep Recommendations are what has impacted on the 85% reduction in SUDI (Sudden Unexpected Death in Infancy) which includes SIDS & Fatal Sleep Accidents.

Red Nose has this information.

Although many studies have identified underlying risk factors for SUDI, the causative or pathophysiological mechanism that make some babies more vulnerable than others still remains uncertain. However, it is currently widely believed that SIDS is multifactorial. The Triple Risk Model is useful for understanding why SIDS may occur with particular babies and why it is important to follow the Red Nose safe sleeping practices when caring for every baby. This model suggests there are three interacting factors: when all three are present, SIDS is more likely to occur.

See information about Triple Risk Model here:
https://rednose.org.au/article/why-are-safe-sleeping-recommendations-so-important

How old is your baby?
Remember the Safe Sleep Recommendations.

Always place baby on back for sleep.
Keep baby’s head & face uncovered.
Keep baby smoke free.
Provide a safe environment day & night
Sleep baby in same room as adult caregiver for first 6 months
Breastfeed.