Are Saline and Silicone's Implants Shells the Same Thing?

Yes. The outer shell of the two types of implants are virtually identical except for the valve which is present in the outer shell of a saline filled implant and which is absent in a silicone gel filled implant.

The shell of saline and silicone gel implants are similar but not exactly the same.  The shell of the silicone implants are essentially "thicker" than it's saline counterpart.