Have the oceans dissolved water vapour?
The answer is no, yes and then, perhaps, no.

No: water vapour is not "dissolved" in the oceans, rather it becomes part of the oceans through a phase change from vapour to liquid (possibly via an intermediary stage as ice). The process of "dissolving" refers to a substance entering a "solution", which is defined as stable mixture of two or more substances in which the state of the solution is determined, generally, by the solvent (the liquid water in this case). For example, see the wikipedia article on "solution". When water vapour enters the ocean, it is just adding to the volume of liquid water. Water vapour bubbles suspended in the ocean is another issue. When a gas is dissolved in a liquid, it ceases to be a gas. So we do not have "O2 gas" dissolved in the ocean, we have O2, which is a gas in the atmosphere, present in the ocean as a solute.

Yes: on the other hand, there is continuous exchange of water between the atmosphere and the ocean: sometimes water passes from the atmosphere to the ocean, sometimes the other way around, depending on the weather conditions. This is nothing to do the the process of being "dissolved", but, if the question is motivated by an interest in the exchange of compounds between the atmosphere and the ocean, this cycling of water between the two, which is described more below, will be of interest.

Finally, perhaps, no: the water vapour in the atmosphere is not in equilibrium with liquid water in the ocean (see wikipeadia foe discussion of equilibrium between liquid and gas phases). Generally speaking, the partial pressure of water vapour above the ocean will be below equilibrium, so there will be an evaporative flux of water from the ocean into the atmosphere. The steady evaporation of water from the surface of the oceans is balanced by precipitation (rain, sleet and snow) out of the atmosphere which falls on the oceans or falls on land and then drains into the oceans (see The Fundamentals of the Water Cycle).