On a system with MAX96705 and MAX96706 (or any other Serializer/Deserializer), can the serializer have 1.8V on IOVDD and the deserializer have 3.3V on IOVDD or vice versa?
Yes, this will work fine. The only connection between serializer and deserializer is the serial link, which has pre-defined common mode and voltage swing. The Serial Link is unaffected by IOVDD.