According to the Kyma OSC documentation, and my own experiments, I do not believe that the osc message /vcs/play can have multiple arguments. OSC messages with an address in the form of /vcs/<name> are handled as a special case in Kyma. These messages are automatically mapped to Kyma named events. For example /vcs/Foo becomes !Foo, and can be referenced wherever event values are used.
The actual syntax though is slightly different, a channel number is required as the last part of the OSC address. /vcs/<name> is not recognized and will be ignored, based on my testing. The correct form is /vcs/<name>/n, where n is the channel number 1, 2, and so on. So ther example message would actuallu need to be /vcs/Foo/1
Normally OSC messages containing multiple arguments are split into individual messages of one argument. So you would expect /vcs/play, ff to become /vcs/play//1,f and /vcs/play//2,f (See "Kyma 7 User Guide" page 193). However since Kyma treats addresses starting with /vcs as a special case this form does not work.
Based on my quick testing, any osc message whose address starts with /vcs is filtered unless it follows the strict /vcs/<name>/n format, and has only a single argument. This make sense since the intent is to provide an automatic mapping to event values, and event values are by nature scalar variables.
If you wish to send an OSC vector of values then you have to use a different address scheme, something like /foo/play,ff would create two new event values, !osc_foo_play__1 and !osc_foo_play__2. (See "Kyma 7 User Guide" pages 190 & 191)