Just to add some more meat to this, here's a ton of info on which carriers allow this. This is copied and pasted from a NARPM discussion thread from a few years back. Credit is due to original posters; the below is not my info but posted for reference.
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Our company has an administrative person dedicated to making sure our owner and tenant insurance policies are current and in compliance. Here are some things we have learned which may be helpful to other management companies:
State Farm will name management companies as additional insured on the declaration pages and they will name management companies on condo policies as well as single-family homes and townhouses.
SAFECO policies will name management companies.
Allstate will not list management companies as additional insured for condo’s/apartments only. For townhouses and single-family homes, if the owners have a Landlord Package Policy and we are listed as “additional interest”, we are covered. In the full policy copy the owner receives, the following statement shows we are covered: section 6. “Insured person(s)” e) any person or organization while acting as your real estate manager for the residence premises.”
For Erie policies, it depends on what type of policy they have. The older Ultrasure policies automatically covered management companies but these policies are being phased out. A new policy (replacing the Ultrasure) is called the Ultra Pack Plus and is a commercial policy which can name management companies. Some agencies will list the management companies on the Erie Secure policies and others will not (it seems to depend on their underwriters).
USAA policies usually show us as covered if we are listed as “Real Estate Manager”. It is always a good policy to doublecheck.
For companies who only list management companies as additional insured internally, I have found that they will often issue a “certificate of insurance” if requested, that will list the management company for their files.
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Century National uses the additionally insured endorsement codes: DL-2410 and DP-0441 - section 2 only coverage L and M.
American National uses the additionally insured endorsement SD 9041 0989
State Farm uses the endorsement code: “Option AI” and the declaration page should list the property management company as “Additional Insured-Section II only”.
USAA uses the additionally insured endorsement DP-41 but this code only shows on the homeowner's policy not the declaration page received by the management company
CSE Insurance Group uses the endorsement code D041ST1
First American P+C: The property manager needs to be listed on the second page of the declarations under Additional Interest/Additional Insured with the words “Addtl Insrd” next to their company name. If the words "Addtl Insrd" are not written then the property manager is only an additional interest.
American Family Insurance: uses the additionally insured endorsement BP 04 02 01 06
Based on my research the following insurance carriers don’t offer the additionally insured endorsement for property managers: AAA, Geico, Progressive, Allstate, Liberty Mutual.
Farmers agents have told me they do offer the additionally insured endorsement but it only shows on the insurance agents internal files (not on the homeowner or property manager's dec page) so I'm not 100% confident I would be defended correctly if there was a lawsuit.