Yes, the Multiroom (Smart TV) will utilise one (1) of your Astro GO concurrency.

Customers subscribing to Multiroom (Smart TV) can enjoy access up to 4 concurrency (watch 4 screens at the same time) which is shared across one Smart TV device and 3 mobile/laptop/tablet device(s), for limited period only. The default is 2 concurrency per Astro account.