Can a Laser Engraver be used to develop PCB with photoresist?
Yes, you can. What you need to know is the wavelength at which your photoresist absorbs the most energy. This should be specified in the corresponding datasheet of your manufacturer.

There are also commercial products which use laser diodes. I know of one that has 120 mW at 420 nm but different pcb manufacturers may use different photoresists which may require different wavelengths.

If you google Laser direct imaging you will find several commercial products.