Yes - if you restore from the backup the data should be in the backup. If the notes are that important, you should backup the iPad every day .... If you use the app every day that is. Make sure your backup is always current.
If you depend upon an app that heavily, you should always read all of the information that is available so that you know what the app does and does not do. According to this text which I copied from the app description page in iTunes, it also offers "backup to a single file for off iPad storage". That sounds to me like you can store the notes/app data on your computer as well.
If the app works with file sharing - which it probably does - you can transfer the files to iTunes and then to your computer for safe keeping as well.
You can use "Open In" in other apps or iTunes to send PDF files to Note Taker HD for annotation.
Other features include:
- Support for the retina display on new iPads
- Pages organized into documents and folders
- Typed blocks of text with optional borders
- 60+ highly customizable shapes
- Insert and crop images from Photo Albums, Pasteboard, or the iPad camera
- Custom backgrounds from images or PDF pages
- Free templates and clip art on the support web site
- VGA/HDMI/AirPlay support with zoom and pan
- Wrist guard to avoid inadvertent touches
- Layout variations better suited to some left-handed users
- Optional fields in output footers like in a word processor
- Extensive built-in help
- Smooth and crisp ink on screen and in PDF output
- Share editable copies of your documents with others
- Backup to a single file for off-iPad storage
- Password protected folders
- Support for the iOS Data Protection API
- Full-screen preview mode
- Copy/Cut/Paste between pages
BTW ... Just so that you know - the app itself is not contained in the backup. If you are using iTunes, you would have to sync the app back to the iPad or download it again from the App Store in the event of some disaster with the iPad. The app data is stored in the backup but not the app itself.