To see if the checkbox was checked:
SELECT name, is_auto_executed FROM sys.procedures WHERE name = 'sp_ssis_startup'
If 'is_auto_executed' is 1 then it was checked at installation.
To change the value of 'is_auto_executed' to 1 when it wasn't enabled at installation:
EXEC sp_procoption
@ProcName = 'sp_ssis_startup',
@OptionName = 'startup',
@OptionValue = 1;
This should answer your question.
Greetz,
Ken