Yes they are.
From the motherboard's memory QVL page (https://www.asus.com/us/Motherboards/TUF-Z270-MARK-1/HelpDesk_QVL/),
The QVL labelled "Z270_PRIME_TUF_STRIX_Memory_QVL", updated 2017/02/24, (http://dlcdnet.asus.com/pub/ASUS/mb/LGA1151/TUF_Z270_MARK1/Z270_PRIME_TUF_STRIX_QVL.pdf?_ga=2.64658728.627901775.1498259541-1428616915.1495995095) mentions:
"
DDR4 3600 Qualified Vendors List (QVL)
G.SKILL | F4-3600C17D-16GTZ | 16GB(8GB*2) | 17-18-18-38 | 1.35V
G.SKILL | F4-3600C16D-16GTZ | 16GB(8GB*2) | 16-16-16-36 | 1.35V
G.SKILL | F4-3600C15D-16GTZ | 16GB(8GB*2) | 15-15-15-35 | 1.35V"
These are the RAM sets mentioned:
F4-3600C17D-16GTZ:
https://www.gskill.com/en/product/f4-3600c17d-16gtz
F4-3600C16D-16GTZ:
https://www.gskill.com/en/product/f4-3600c16d-16gtz
F4-3600C15D-16GTZ:
https://www.gskill.com/en/product/f4-3600c15d-16gtz
Note also that RAMs not listed in the QVL may also work/be compatible (it's just that, it wasn't tested by the manufacturer due to the sheer number of RAMs and limited amount of time to test out all possible configurations).