No you cant use the ULN2803A in that way, as its a current sink not a current source.
The relay boards shown in the above diagrams all use 5v on the opto-isolator inputs, and sink the current using the in pins which are connected to the pi gpio, this results in 2 problemsWhy do you need to use a ULN2803A at all considering the relay board already has a 817c optocoupler. Won't this prevent EMF feedback?
No diagram but from the way the board seems to work 5v from arduino input used to power led side of opto-isolator with a common ground and 5v supply on relay board used to power relays via transistor in opto-isolator
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