Hi,
CCA and Special Allowances are taxable to the employee. However, if you give the medical component as Medical reimbursement, wherein the employees submit bills, the same is tax-free upto Rs. 15000/- per annum.
Regarding your query as to the circumstances under which you can include these under salary heading: Both CCA and Special allowances are taxable in the hands of the employee; it is the organisation's call if they want less tax burden for the employees or they have more tax friendly salary packages devised.
Hope this solves your query. One more thing you could have done was done a search on this site itself; your query would have been solved long time back. There is a lot of material on CTC available on this site.
Warm Regards,
Anuradha Zingade