My experience so far is that some vendor solutions that rely on DBs are not cloud ready. If the apps aren't cloud ready then putting the DB in the cloud isn't going to work very well.

In some cases we can find ways to install and configure the apps in a way that is sympathetic to cloud deployment. The question then becomes whether the vendor will support that configuration. Again my experience is that the vendors are keen to have a case study showing that their app can work in the cloud.

Where they are unlikely to compromise is where there is an SLA involved. Some of the machine specs are considerably higher than instances available in the cloud.

Cloud DBs do offer considerable advantages for many scenarios. Belief in technical robustness lags some way behind actual technical robustness