Are deterministic formula fields auto indexed by salesforce platform?

We are have developed a managed and one our customers have installed it. To improve query performance we are planning on adding custom indexes and currently investigating which of those will be useful.  In this scenario, do our cilent requests addition of custom field or do we do it ?

Do we have to repeat this process with every client that installs our package or  Are custom indexes portable?

Are deterministic formula fields auto indexed by salesforce platform?

Per Standard Suport's directive to me this week, I am posting this HERE to get fields Indexed.  Why Support would make me talk to the Developer's Community to get Support to index my fields?  I have no clue.

These are all Date fields.  I cannot mark them Unique External IDs.


Webinar Attendance     Case 10812794
https://help.salesforce.com/apex/HTViewCase?id=5003000000V5gLwAAJ
INDEX:
Registration_Date__c
Workable_Opp_Date__c
Join_Time__c
Leave_Time__c


Lead Sources     Case 10812807
https://help.salesforce.com/apex/HTViewCase?id=5003000000V5gPoAAJ
INDEX:
ead_Source_Date__c
Cake_Conversion_Date__c
Override_Date__c (not specifically a problem yet, but anticipated in the future to be)


(Person) Account     Case 10802220
https://help.salesforce.com/htviewcase?id=5003000000V4wjaAAB
INDEX:
Webinar_UTP_First_Attd__c
Webinar_UTP_Latest_Attd__c
Webinar_UOC_First_Attd__pc
Webinar_UOC_Latest_Attd__pc


(Exact Target) InidividualEmailResult     (ET) Case 01156464
ref:_00D00hftv._500A0MEwr9:ref
INDEX:
--all Date fields--