It depends -- many tapes have a sort of a filesystem on them that contains a table of contents and an offset to each specific file on the tape. On AIT tapes it is actually flash media in the tape itself called MIC.
If netbackup zeroed out the tape then the it will have had the number of files on it and their offsets wrong relative to the data you actually want to restore. For instance -- this is a tool that says it recovers an ait tape from the sort of situation you're in right now. I've never used it but it sort of illustrates the situation you're in.
If the data is really important, you may want to stop messing with the tape and send it to a facility that specializes in this sort of thing before things get worse. This is likely a common situation so it is likely that if there is anything to recover they will find it and recover it (and quickly)
Lastly, depending on the type of tape and tape drive -- serpentine or helical, you may have either randomly corrupted your data or only corrupted the first bit of it. I'm not sure if modern DLT tapes have a different erase head but it is possible that random chunks of the data have been erased by starting at the head of the tape.