Can data techs see the individual files in a dmg file?

The drive on my MacBook failed recently and I really need to get my data back. I am hesitant to take my hard drive in for repair/recovery for fear that, somehow, the techs will be able to see the individual files in a dmg file I keep on my laptop. They will be extracting data by taking my drive apart (to bypass bad sectors?), rather than by just using software. What do Dmg files look like from a tech's perspective? Can they see file names? Preview images? Or, will they simply see a dmg file? Thanks for your time!