Off-site linking:
Video-overlay extensions may not contain links of any kind.
Panel extensions must submit a whitelist of domains requested for off-site linking.
Off-site links must be related to the extension’s core functionality.
Off-site links may not refer users to sites that deliver functionality effectively similar to that available on Twitch.tv.
Extensions may not encourage or reward users for consuming Twitch content on a site other than Twitch.tv.
Extensions may not encourage or reward users for taking specific actions outside Twitch/Amazon properties.
Probably not no. You would promote people leave Twitch…
Please go read the Guidelines https://dev.twitch.tv/docs/extensions#guidelines-and-policies