From NOT a DBA ...
sounds like what you really need is an Oracle "sequence". I have implemented similar as follows:
CREATE PROCEDURE dbo.nextval @sequence varchar(28) AS
SET NOCOUNT ON
DECLARE @sql nvarchar(100), @scope_identity int
SET @sql = 'INSERT ' + @sequence + ' default values SELECT @scope_identity=SCOPE_IDENTITY()'
BEGIN TRANSACTION NEXTVAL
SAVE TRANSACTION SEQUENCER
EXEC sp_executesql @sql, N'@scope_identity INTEGER OUT', @scope_identity OUT
ROLLBACK TRANSACTION SEQUENCER
COMMIT TRANSACTION NEXTVAL
SET NOCOUNT OFF
with a created table (@sequence) that contains only an identity column, this concept allows any number of "sequences".
The upside: locking is minimized or eliminated, the table size never changes (more or less)
The downside: there maybe gaps in the sequence
SQL Server has this "useful" feature, it never rolls back an identity value assigned, so even though the transaction is rolled back the identity value is not