All synchronizations for real-time processing is in the Cakewalk (and other DAWs) core. I do not know any external API which can influence it. I mean such requests is better to discuss on Cakewalk forum.
The following is IMHO, based on some (small) experience with VST plug-ins (writing):
when the transport is not running, Cakewalk/REAPER (I have not tested that with AL) do not advance musical time. All plug-ins (f.e. soft synth) have access to the tempo and current musical time, but these numbers are constant and taken from the current project time cursor position. In other words when time cursor stay at zero, every time plug-in is called it is at the beginning of the first measure.
I am in progress of writing some "pattern player" (a kind of auto-accompaniment, I know at least one separate Yamaha compatible real-time player, OMB, but nothing in VST format). And I have to deal with "musical time" separately for playback/recording and with transport stopped. In the second case I have to "generate" continuous musical time myself (based on audio time and current tempo from the DAW). I guess other musical time based plug-ins do the same.
So doing MIDI syncing with transport stopped is at least hard. It may be not possible/feasible at all, running musical time in stopped state potentially can confuse plug-ins up to malfunction.