"Subject to" means that it is likely to be affected, or is already affected by something.
The finance department is subject to random inspections by the auditors.
This means that the auditors often inspect the department.
On the other hand "exposed" to means it would be affected if the event occurs.
The company is exposed to losses if the stock market crashes.
This means that if the stock market crashed, the company might lose money.
So in your situation are they at risk and therefore exposed. Or are they already affected, and so subject?