You can create two policies if you wish and that will work but there is no point backing up the same data twice. Accelerator is like a Synthetic backups anyway, so there is no point in doing an Accelerator Backup with Synthetic! (although you can't do both in 1 policy anyway)
Mark Solutions did a nice little one line summary of these methods in a previous post:
https://www-secure.symantec.com/connect/forums/difference-between-synthetic-backup-optimised-synthetic-backup-and-virtual-synthetic-backup
1. Synthetic - done without network transfer and make a whole new image
2. Optimnised Synthetic - done without network transfer and synthesises and new image but adding de-dupe pointers only
3. NetBackup Accellerator - small amount of data transfer from the client and synthesises a full backup