The Rebbe supports speaking at non-religious events if done carefully, ensuring it won’t be seen as endorsing their views. He encourages using every opportunity to inspire Yiddishkeit, as such efforts usually bear fruit. He also urges follow-up on family purity and tefillin, and mentions praying for them at the Ohel.
https://www.torahrecordings.com/rebbe/004_igros_kodesh/adar/938