There is a pretty good book by sharon Foga : getting started with apache OFBiz Accounting.
I do not recall her reading data from a different accounting system, but she covers the accounting so you can become familiar with it. She also gives a good example of webtools (ofbiz has a utility called webtools).
You can read and write data using web tools, but it is pretty specific about the format.
I was able to interface OFBiz to our product using my own routines. You may find that is the easiest way to get data into your system. I create products, supplier records for the products and min qty records using a java routine.
Good luck.
Joel Fradkin