ok so you are trying to execute stored proc inside join. Also the IF statement should be outside.

If you can get the date from this stored proc and then count the records.

I am not sure the data set returned but you can.

IF @checker is not null

BEGIN

INSERT INTO #temp

(

column1

,column2

,....

exec [dbo].[GetEmployees]

@parameter1,

@parameter2

END

ELSE

BEGIN

INSERT INTO #temp

(

column1

,column2

,....

exec [dbo].[GetEmployees]

@parameter3,

@parameter4

END