The current workaround is to re-import the dg before adding any disk, then the addisk would fail with error:

# vxdg init testdg ibm_shark0_3
# vxdisk set ibm_shark0_3 clone=on
# vxdisk -o alldgs list |egrep "ibm_shark0_3|ibm_shark0_4"
ibm_shark0_3 auto:cdsdisk ibm_shark0_3 testdg online clone_disk
ibm_shark0_4 auto:cdsdisk - - online
# vxdg deport testdg
# vxdg import testdg
# vxdisk -o alldgs list |egrep "ibm_shark0_3|ibm_shark0_4"
ibm_shark0_3 auto:cdsdisk ibm_shark0_3 testdg online clone_disk
ibm_shark0_4 auto:cdsdisk - - online
# vxdg -g testdg adddisk ibm_shark0_4
VxVM vxdg ERROR V-5-1-18510 Device ibm_shark0_4 is a non-clone disk.
Adding a non-clone disk to a clone diskgroup is not allowed

Under the certain circumstance where there might be clone disk and non-clone disk co-mixed, and the dg couldn't be re-imported once the dg is deported.
To simulate this issue, we can.
1. Create a dg.
2. Set clone flag on the exist disk in the dg.
3. Add a non-clone(normal) disk into the dg. (there should be no issue at this time)
4. Deport the dg.
5. Import the dg  and then the error will occur.

Below is the output of the above procedures.

# vxdg init testdg ibm_shark0_3
# vxdisk set ibm_shark0_3 clone=on
# vxdisk -o alldgs list |egrep "ibm_shark0_3|ibm_shark0_4"
ibm_shark0_3 auto:cdsdisk ibm_shark0_3 testdg online clone_disk
ibm_shark0_4 auto:cdsdisk - - online
# vxdg deport testdg
# vxdg import testdg
VxVM vxdg ERROR V-5-1-10978 Disk group testdg: import failed:
Disk for disk group not found