The IDE-SCSI driver is an obsolete driver which was used to access ATAPI devices through the Linux SCSI system. The driver's nature generated some confusion among users, who might not understand why an IDE (ATAPI) device would operate with a SCSI device driver. Basically, the cdrecord package and other tools have historically been SCSI-specific, and so the IDE-SCSI driver was created as a compatibility layer to allow applications written for SCSI devices to access ATAPI drives.
However, this led to various complications later on: for instance, some devices such as DVD drives would need IDE-SCSI mode for some features (like CD writing) and normal ATAPI mode for others (like DVD access) - meaning the driver would need to be loaded or unloaded for each usage. These problems and others led to support for the driver being removed in the 2.6-series kernels. Applications are now expected to support the ATAPI devices without SCSI emulation.