UNION SELECT, parallelization and IDENTITY

There are four identical staging tables:

CREATE TABLE s_table_1
(
      id INT IDENTITY(1, 4) NOT NULL PRIMARY KEY CLUSTERED
    , some_data NVARCHAR(100)
);

CREATE TABLE s_table_2
(
      id INT IDENTITY(2, 4) NOT NULL PRIMARY KEY CLUSTERED
    , some_data NVARCHAR(100)
);

CREATE TABLE s_table_3
(
      id INT IDENTITY(3, 4) NOT NULL PRIMARY KEY CLUSTERED
    , some_data NVARCHAR(100)
);

CREATE TABLE s_table_4
(
      id INT IDENTITY(4, 4) NOT NULL PRIMARY KEY CLUSTERED
    , some_data NVARCHAR(100)
);

Subsequently, they are used in a view:

CREATE VIEW s_table AS
              SELECT * FROM dbo.s_table_1
    UNION ALL SELECT * FROM dbo.s_table_2
    UNION ALL SELECT * FROM dbo.s_table_3
    UNION ALL SELECT * FROM dbo.s_table_4;

The rationale behind this structure is to be able to stage data in four parallel streams to make use of multi-core CPU on the server (data comes from a large flat text file from a local drive; reading that file it is much, much faster than writing rows to target table; splitting this to four streams gives me over 3x faster ETL and I need this to be fast)

I need the ID values to be unique across all four staging tables - this is why I created them as IDENTITY(N, 4) where N is 1, 2, 3 or 4, respectively.

Is this setup "risky" in terms of uniqueness? I mean, is there any chance that one of those four IDENTITY columns clashes with another one?

Any hints welcome.

SQL Server 2012