Surya,
You can send Stock Transport orders across, but you do not need to perform Availability checking in SCM in the supplying plant if you have a reason not to do so.
For availability checking in 1000, you can perform this task in either ECC or in SCM. You stated you didn't want Production order ATP performed in SCM; I also assumed you also didn't want your STO ATP in the supplying plant performed in SCM as well. In this case, do not create an integration model for ATP in the supplying plant 1000. Stock transport orders can still go across, and you can perform planning in SCM; you just don't do ATP in SCM.
Best Regards,
DB49