Electronic filing of 1099s is not supported by NetSuite, unless you have the Premier Payroll module (=$$$) on your instance. I have zero experience using that module, so have no idea if you can file 1099s for vendor contractors from therein as well, as opposed to 1099 employees.
We carried out our 1099 activity last year by generating 1099 reports from NetSuite, and then manually punching data from those reports for all vendors into a software called ‘W2 Mate’ for electronic filing.
Among so many other disappointments, this is yet another frustration with NetSuite; even QuickBooks offers electronic filing capability.