If you need an exemption, then you must be in removal proceedings. You could appeal, but what would be the legal reason for not submitting the exemption to begin with? It would probably faster to reapply. However, given that you already made a mistake, wouldn't it be wise to retain counsel? If you are in removal proceedings, don't mess around hire an attorney.
Each situation and case is fact specific. So the short answer to your inquiry is "it depends upon the facts." I am not sure what your reference to request for exemption involves. Most situations/applications where there is insufficient information submitted with the I-130 for USCIS to determine whether the familial relationship exists, they will send out a Request for Evidence or RFE.
You then usually have 89 days to submit the requested information or USCIS will deem you application abandoned and deny the petition.
Your best bet is to consult with an experienced immigration attorney who can provide you with proper legal advice.
Stanley Dale Radtke, Esq. 415-974-0306. The statement above is general in nature, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship