Aluminum electrolytic vs. tantalum capacitor for buffering SAR ADC Ref input
They don't appear to be much different electrically. 

Tantalums are physically smaller and SMT, which is a big advantage in some applications. 

I think you'll be fine from the pov of the ADC if you use that, perhaps with 1uF ceramic X7R in parallel close to the ADC. 

Minor nit- I would not call a bypass capacitor a 'buffer'. The OPA350 amplifier is the buffer.