Daisy-chaining for two pedals is usually OK - just add up the current consumption of the two devices (it'll be underneath the pedals and given in milliamps (mA)), as long as you're not to pull too much current through the power supply then you should be OK...
Edit: Just checked the specs and the Onespot delivers 1.7A (1700mA), which is plenty!
According to their manuals the Spectradrive draws 250mA and the Polytune draws 45-50mA, so you're nowhere near the 1700mA limit!
One caveat though is mixing analogue and digital devices from the same PSU can sometimes introduce noise, but I don't remember having that problem when I ran the onespot.