I have some polk speakers in my car that have a center like you describe. I used my hot glue gun with 3m yellow glue stick and it seems fine since I fixed it 2 years ago. My sub surround came delaminated from the main driver and I repaired it today using Lepage contact cement. With contact cement only a vey thin layer is required on each surface , I guess I will find out soon enough.
Drivers are designed to be a rigid as possible while remaining light weight. I would think there is less flex at the middle than at the outmost portion of the driver.