[….] Every game will be playable offline, and many games will offer support for game controllers. Because subscribers can play [….]

Above you see an excerpt from Apple's press release, so by the look of things, there will be partial support for controller on Apple Arcade.

Apple unveiled a new subscription service called Apple Arcade at the company's "Show time" event. It will show up as a new section of the App store and will be Available in 150+ countries.

The games released on Apple Arcade will be exclusive titles and will not be available on other Services. Unlike the recently treding cloud streaming gaming services like google's recently announced "stadia" or services from other competitors like Microsoft or Nvidia, Apple Arcade games will run natively on iOS devices.

Subscribers will be able to access all games and future updates with one subscription. Parents will be able to check on their kid's playtime with the "screen time" feature.

Apple's official press release on apple arcade