There are two distinct failures when reading DVD discs. One would be the laser failing to lock onto the wavelength of the disc. This would be characterized by your drive's standard "Unable to read disc" error after a long time possibly 90 seconds.
The other would be the drive reading the identification bits at the beginning of the disc, not recgonizing the disc type, and rejecting the disc. Same error as above, but it would occur almost immediately.
AFAIK -R drives cannot write custom identification headers. (Certain) +R drives can. 'DVD-ROM' would be the same header that commercial pressed discs have. By default, -R drives burn 'DVD-R' for -R and 'DVD-RW' for DVD-RW. +R burns 'DVD+R' and 'DVD+RW'.