Well, there is the documentation and then there is also experience :)
Yes, the backup needs to process the exclude_list against the filelist found on the client. But computers are built to be able to do such processes. RIGHT?
On the other hand if 30 files are always active and you don't exclude them then the backup will slow down due to the constant retries of attempting to capture the files for the image.
If you have a lot of servers that you are backing up and using multiplexing then you will not see the difference of a client having 30 exclude statements or zero exclude statements even if you are backing up thousands of clients. Best practice is to try to expand the exclusion to the entire filepath\ filename.
Here is documentation directing to place the files in the exclude lists
In-depth Troubleshooting Guide for Exit Status Code 1 in NetBackup Server (tm) / NetBackup Enterprise Server (tm) 6.0
http://ftp.support.veritas.com/pub/support/products/NetBackup_Enterprise_Server/278554.pdf