In chair form of cyclohexane the C-H dipole moments cancel out each other but in boat form i don't think all dipole moments will be cancelled out. Also if boat form is polar then what will we say overall about cyclohexane is it polar or nonpolar?
The boat form is ~6kJ/mol less favourable, making cyclohexane 99% chair at RT. So whatever small polarity the boat form has (after all, its a plain alkane, and still rather symmetric), you need to divide that number by a hundred.
Btw. the twist conformation is not as unfavourable as the boat form, but it is also too symmetric to have any dipole moment.
(https://en.wikipedia.org/wiki/Cyclohexane_conformation says CH is even 99.99% chair)
Being nonpolar does not require having the zero dipole moment.
Enough is being much closer to having a zero dipole moment than to having the a strong dipole moment. It applies also to parts of the molecule.
E.g. carbon dioxide has zero permanent dipole moment, yet liquid carbon dioxide is rather polar solvent due its polar bonds.