Froom 2017:

The utility of the Oncotype DX in decision making for treatment of invasive lobular carcinoma (ILC) has not been investigated as the results reported by Genomic Health are largely in a population with invasive ductal carcinoma (IDC).

There is a lot of advocacy going on about lobular cancers. I would call the company (no longer Genomic Health, now called Exact Sciences apparently) for information on testing for lobular cancer.

I don't know the accuracy/validity of any Oncotype test for predictions about lobular cancers but Oncotype could give you more information and their phone number is:
1(866) 662 6897

I'm inclined to think that they wouldn't offer a test unless they've verified the accuracy of the results and conceptual value of the test but, again, they'll be able to answer your questions. As should your oncologist who should be the person to query further as well. And ask your doctor if any other test(s) would be valuable whether covered by insurance or not. [I've found that doctors think more in terms of insurance coverage than I do. I want to know if ANYthing that might be important and I'll decide about the financial stuff myself.]

I hope you feel better that a negative lymph node is in fact good news.