I2C Bus With Conflicting Pullups
Usually the I2C bus requires only two pull-ups, on SCLK and on SDA. If one of your devices has those pull-ups, then it may be just enough. You can look into RPi GPIO datasheet to see how much current it can sink (as well devices datasheet), therefore having two slave devices, each with its own pull-ups is not a good idea - the overall resistance can become too low, thus the bus current over max. allowable.