Yes, that setup should work.
Serato DJ Pro works natively with the Roland DJ-505, so you can keep using your controller normally with Serato.
Emulator can run alongside Serato on a touch device and act as an additional control surface, expanding what your hardware controller already provides. For example, you could create custom layouts with extra pads, hotkeys, macros, effects triggers, or other performance controls mapped through MIDI.
The idea is not to replace your DJ-505, but to add an extra control layer that gives you more flexibility and screen-based controls.
Also, Emulator can be fully controlled with the mouse (one control at a time, since a mouse is not a multitouch device), so you don't even need a touchscreen device to start experimenting. You can begin creating and testing your templates using only the mouse.
If you need help setting things up or creating your template, just let us know and we will gladly assist you.
Please continue this thread for any related support so we can help you through the setup process.
