does a z270 support intel i3 6100 skylake

Solution
Judging by CPU support for some Z270 boards (for example, https://www.asus.com/us/Motherboards/PRIME-Z270-A/HelpDesk_CPU/), yes you should be able to use Skylake CPUs on Kaby Lake boards.

They're the same socket after all.
yes. the socket is same.
but if you used i3-6100 on Z270, notice two results
first, DDR4 default is 2133 not 2400
second, not support intel optane