Is Nethandicap an official USGA handicap index service?

Absolutely :)

We have been providing USGA Handicap service tracking since 1999.

Starting January 2015 Nethandicap became Nethandicap.com Corp and has invested in redesign, improvements, new hardware, new technologies and an ambitious roadmap.

For members that join clubs (located within 50 miles of city bounds) and enter minimum rounds, each effective date, handicap is recalculated based on USGA rules.

For Canadians we follow RCGA rules , which are similar to those in UK and USGA.