Using ODM 8.10.2 on z/OS, I have a partner team that is getting spreadsheets from the business, and loading to Decision Tables in Rule Designer, then syncing to Decision Center. The problem they have is that the data in the spreadsheets received from the business sometimes has spaces at the end of the fields that causes issues at runtime. We would like to know if we can remove the spaces using Java API.

you should be able to use the Java API to edit the decision table content. There are two sample project closely related with your topic:

ODM_HOME\teamserver\samples\servercopydecisiontable

ODM_HOME\teamserver\samples\serverbaselinesdiff

I think the most important API in the sample code that you should pay close attention is this class "IlrDTModel":

https://www.ibm.com/support/knowledgecenter/SSQP76_8.10.x/com.ibm.odm.dserver.rules.ref.designer/html/api/html/ilog/rules/dt/model/IlrDTModel.html

From this document, you can find following statement:

This interface provides the API to do the following for the decision table or decision tree model:

create the structure

edit the content

visit the model

Therefore, you should be able to use this API to edit the decision tables. You can find much more sample code in the sample project.