Your employer's thinking that there is an obligation to inform Worker's
Compensation may be well-intentioned -- although, misinformed.
On the other hand, your employer may be trying to delay, or avoid, parting with the cash.
Either way, your belief that your vacation pay has nothing to do with
your disability is absolutely correct. This is because you earned
the vacation time prior to your becoming disabled.
The fact that, you are on disability when you receive a cash payment
for the vacation time -- should make absolutely no difference in your
original, or continued, eligibility for disability benefits
of any sort.
The only exception of this would be if you are receiving Supplemental
Security Income (SSI) benefits -- SSI eligiblity requires that a person
be low income -- in addition to having a disability.
I recommend you contact the The California Department of Industrial Relations -- Division of Labor Standards Enforcement
for assistance in this matter.
They should be able to quickly set your employer straight regarding the obligations to pay you for your accrued vacation time.
Let me know if you need more input. If not, thanks for the
opportunity to assist you... I would really appreciate your honoring my
efforts by 'pushing the button' and Accepting this answer. Adding
a bonus -- should you wish to do so -- is always warmly welcomed.