If you check the regular licensing terms, it states as “Use, by you or one client, in a single end product which end users are not charged for.”
It means that customer agrees on using the purchase on a single end product and that too not for commercial use. If your custom who purchased is going to use as part of same product in which he has integrated your item, then its ok. But if he has multiple/different end products where he would be using it then he would require to buy regular license for each of his end product/project.
Also, if these product are going to be used as SAAS application of similar where customer will be charged, the customer requires to buy an EXTENDED license for each end product.
In your case as you have an admin theme i doubt if he is building any kind og SAAS software. where he would require to have multiple sub-domains for users using his software. In this case, i think if he buys an extended license and keep it used as part of sub-domain for same end product, that should work.
People, please read my comment and clarify me as well if i am wrong at my understanding else support 
theem’on