The scheme should work. The reset pin goes (internally) to the base of a PNP transistor and so won’t be forcing any voltage onto the pin. I’ve read that the reset pin is TTL compatible and so any TTL logic 1 voltage should keep the 555 out of reset, any voltage < 0.8v will reset it. Current draw from the pin should be < 0.1 mA. If you wanted to, you could use a 5v Zener in place of the “lower” resistor in the divider.
Any reason for using a 555 vs a comparator (LMx39 series) ? What stops the LDR from immediately retriggering the 555 and thus the Arduino ?