Icon Picker has native support for Redactor (opens new window). You're required to nominate an Icon Picker field to be used in your Redactor fields, so that you can configure the appropriate icon sets available.
Firstly, you'll want to edit your Redactor config files (opens new window), and be sure to add icon-picker to the plugins array.
{
"plugins": ["icon-picker"]
}
Next, create an Icon Picker field with the appropriate icon sets you'd like to use. Take note of this field's handle. Either head to Settings > Icon Picker in the CP, or add this to the configuration (redactorFieldHandle).
You'll now have an Icon Picker button in every Redactor field that uses the config.