So, it appears that the drive is capable of reading disks but has a bias against the Bento disk.
As I recall the Bento disc is not bootable and therefore will not show up on an option boot situation.
However, the initial presenting problem did not involve booting but the failure of a drive to recognize a particular disc when it was inserted. In an optical drive each media type, DVD, DVD+/-R, DVD+/-RW, CD, CD-R, CD-RW uses a unique read laser and a unique write laster. Therefore it is quite common for one laser to burn out rendering the drive unable to read that particular disc type, but still work normally with all other types. In fact it is rather uncommon for an optical drive to fail at reading all media types. Your Snow Leopard disc is a DVD (the data is mechanically stamped onto the disc) and chances are your Bento disc in addition to not being a bootable drive is a DVD +/- R and the read laser for DVD+/-R is burned out. The solution, the only solution in fact, is a new optical drive. It is up to you whether to replace the internal optical drive but my suggestion would be to buy an optical drive in an external enclosure. A USB 2 connection is more than fast enough to support an optical drive, but if you have extra money to spend firewire or even Thunderbolt connections will work.
