MCP3004/3008 maximum voltage on ADC pin
Yes, it will be safe and, the digital output will be limited at full scale. 

Also be aware that there are offset and gain errors in the ADC that will make the reliable range for extracting a meaningful digital value a few tens of milli volts within the nominal range of 0 volts to 3.3 volts i.e. you can’t rely on the full scale range being perfectly 3.3 volts.