Same problem here
I think that monit doesn't support the character ':' as part of the name of the device, before 3.0.68 the mounted filesystems folders was based on UUID, now on the device name. The problem is that all the mdamd array are "MACHINENAME:ARRAYNAME" so every time you mount a raid software device, there is this error.
Already tried omv-mkconfig monit but it won't change anything
This is my opinion and sorry for my bad english