Not really. The only thing we saw in 2008 that might loosely be called a marina is in Nuku'alofa, Tongatapu. At the main harbor there are a dozen of so berths, stern-to. Protect lines well to prevent rats, as the rats are quite large and plentiful in those rocks at your stern.
We arrived in Vava'U and visited almost every island southward through the Hai'pai Group, ending up at Tongatapu for a month. Never saw any other "facility" that might be construed as a marina except the main harbor at Tongatapu. Haven't read or heard of one being built since our last visit to Tonga
Amel SM2 #387