Is money obtained from Google Wallet—by repeatedly sending small verification amounts (less than $1) and accumulating them without directly linking a bank account—considered unlawful (haram) or permissible (mubah)? This is asked knowing that this amount is insignificant to the company and that I have the same amount obtained by this method in my Google AdSense account.

What you are doing is a circumvention of the company's rules and an unlawful appropriation of money, which is forbidden by Islamic law. Your mere claim that the amount means nothing to the company does not justify this act. Furthermore, attempting to seek religious edicts to legitimize fraud only makes the matter uglier and more prohibited. What you mentioned regarding the amount being in your Google AdSense account has no bearing on the issue of seizing the money, because you joined the account by your choice and were aware of its systems and conditions, and the company did not wrong you. The concept of "seizing property" has its own conditions and contexts that do not apply to your situation.