A Newtonian is a reflector but not all reflectors are Newtonians. A Newtonian reflector mounted on a Dobsonian mount is just that. That just means the mirrors need to be properly aligned. How often any reflector needs to be collimate depends on several things but mostly how securely the mirror cells hold their positions. All this movement can cause the mirrors to slip a little in a cell.
Some reflectors have their primary mirror secured in the cell with glue.
This might keep the mirror from shifting in the cell but the cell itself can also shift. A well-built reflector will stay in collimation pretty well during use. Most will even hold collimation when the tube is moved or transported. The secondary almost never needs adjustment once it is properly positoned and secured. I thought all reflectors need their mirrors adjusted, regardless of mount.