Blue Team enemies (Spoilers)

After watching the launch trailer today, it has muddied the water even further as to whether Chief sides with the forerunners. In the latter half of the trailer, Chief and Co are fighting the Warden Eternal.
My theory is that they initially fight the Warden and then they reach some sort of compromise. In the Halo 5 Guardians Chief Experience trailer, the Warden and Blue Team are seen conversing.

Thoughts?