For Guid primary keys the client usually sets it, there’s no built in way in OrmLite to fetch a RDBMS generated Guid which is specific to SQL Server 2005+ and required non-standard SQL which you’d need to drop down to use Custom SQL to access.
To use OrmLite to generate the Insert you’ll need to manually modify the generated SQL and read the Scalar OUTPUT with something like:
var obj = new Table { ... };
using (var db = OpenDbConnection())
using (var cmd = db.CreateCommand())
{
cmd.GetDialectProvider().PrepareParameterizedInsertStatement<Table>(cmd,
insertFields: OrmLiteUtils.GetNonDefaultValueInsertFields(obj));
cmd.CommandText = cmd.CommandText.Replace("VALUES", "OUTPUT inserted.Id VALUES");
cmd.GetDialectProvider().SetParameterValues<Table>(cmd, obj);
var insertedId = (Guid)cmd.ExecuteScalar();
}