Yes—one non-porous mixing jug or measuring container can be used for developer, stop bath, and fixer if you rinse it thoroughly between chemicals. The main risk is cross-contamination, especially getting fixer into developer, which can ruin or shorten the life of the developer.

Good practice:

• Use only non-porous containers and utensils.
• Rinse very well between solutions.
• If you’re unsure the container is fully clean, pre-rinse or “season” it with a little dilute solution of the chemical you’re about to mix, then rinse with clean water.
• Mix in a safe order: developer first, then stop bath, then fixer. That way, any tiny residue is less likely to damage the next solution.

Separate storage bottles for each mixed chemical are still the better approach, but the measuring jug itself does not have to be dedicated if cleaned properly. Avoid porous materials such as some ceramics, since they can retain chemicals.