CO2 gas/solute balance
The CO2 content of the ocean is influenced by both the water temperature *and* the CO2 mixing ratio in the atmosphere above the ocean (as well as by the composition of the sea water - but we'll ignore that for now).
Increasing the temperature of the oceans will decrease the amount of CO2 that can be dissolved in the ocean, for a given fixed mixing ratio of CO2 in the atmosphere. Conversely, increasing the CO2 mixing ratio of the atmosphere will increase the amount of CO2 which will dissolve in the ocean, for a given fixed temperature.
So, it's a question of which factor increases most: if it the atmospheric mixing ratio of CO2 then the CO2 content of the oceans will increase; if it's temperature then the CO2 content of the oceans will decrease.
There has been no serious suggestion that CO2 released from the oceans will cause runaway heating, in our current scenario, because it's is increasing CO2 content which is causing the heating. It is possible, though, that in the past rising temperatures have led to the release of CO2 from oceans (causing increases in atmospheric CO2).
The only important effect I could imagine for CO2 release from oceans in the current scenario would be that CO2 release from the oceans after we stop large-scale CO2 emissions *could* extend the period of MMGW influence. But that would depend on the rate of gas-solute exchange (compared to reservoir size), and the comparative rates of CO2 chemical decay in the two media.