i2c question for using the same address for 2 io expanders to do the same thing

CrossRoads:
The only problem is that I2C is an interaction between master & slave - the slave has to send back an ACK bit as part of the message.
If both devices do not respond identically, there could be problems with the interface getting hung up.

So, likely safe, with the caveat that they all have to be the same device type sharing any one address?