Nested stored procedure and transaction scope - sql-server-2008

Question

I have a main working procedure and an accompanying logging procedure. I'm looking for verification on what my assumptions are with sql server 2008. The desired result is that SP1 does whatever work it can do and calls SP2 along the way to log progress. SP2 work is committed regardless of whether or not SP1 encounters an error that would cause it's transaction to rollback.
Does what I have look safe? Do I need to name transaction in SP2 differently?
------------------------------------------------------- SP1 pseudocode
BEGIN TRY
BEGIN TRANSACTION
-- Do stuff
-- log progress
exec SP2( getutcdate(), 'source_is_sp1','message for progress');
-- Do more stuff
-- log progress
exec SP2( getutcdate(), 'source_is_sp1','message for progress');
-- etc
COMMIT TRANSACTION
RETURN 0
END TRY
BEGIN CATCH
-- error handling not important
ROLLBACK TRANSACTION
return #StepNumber -- not important
END CATCH
------------------------------------------------------- SP2
CREATE PROCEDURE [dbo].[SP2]
#Source as nvarchar(100),
#Timestamp as datetime,
#Message as nvarchar(4000)
AS
BEGIN
SET NOCOUNT ON;
IF #Timestamp is null
BEGIN
set #Timestamp = GETUTCDATE();
END
IF #Source IS NOT NULL AND #Message IS NOT NULL
BEGIN
BEGIN TRANSACTION;
INSERT INTO LOG(LOGTIMESTAMP, SOURCEVCH, MESSAGEVCH)
VALUES (#Timestamp, #Source, #Message);
COMMIT TRANSACTION;
END
END