About backing up Transaction logs
What TSM guy is doing is taking File level backup of mdf and ldf file which does not guarantee point in time recovery. You are correct to say that he should also be backing up folder(s) which holds transaction log backup or other similar backups i.e I:/Log_Backup.
In case of disaster you would always want zero data loss or as much less data loss as possible. If you follow what TSM guy is doing you would be only able to attach database to point when it was Snapshot backed up. But with full backup and log backup you could do point in time restore(depending on level of disaster/corruption) and that would give you no or minimum data loss.


What you can do is you can ask TSM guys to also backup the folder holding full and transaction log backups.