The bulk eraser will probably be just fine but, IMO, it is an unnecessary step. Every DVD authoring application I have used (there are serveral) rewinds the tape to the head and over-writes the existing data. The DLT format was designed to do over-recording and it works very well. The lead-in header on the tape tells any application using the tape where the data is so there is no real chance of accidentally accessing old data left on the tape after the 'current' data.
If you want to erase for security reasons I'm not aware of any problems that the bulk eraser will create for DLT tapes. How effective it will be?