Wireless Adapter compatible with a DOCIS 3.0 Cable Modem

First off, the USB 2.0 WiFi adapter is for your computer, right?  That has nothing to do with Arlo, just how the computer will connect to the Internet for viewing the Arlo interface.  If you're saying that the adapter is for the modem so it can provide WiFi to the house, your best bet is to get your own router and eliminate any issues.  The DOCSIS version won't matter but the provision of WiFi could.

I bought my own modem when Time Warner started charging rent and got one that did NOT have WiFi built-in so a separate router was needed.  This eliminates potential for one thing to take out the whole house network and allowed me to get better equipment than what the ISP supplied.  The only benefit of having an ISP-supplied device is the ability to take a defective unit back to the local storefront to swap for a new one, which is rarely needed.

I'd make sure the modem is just a modem and buy my own router.  That way you have the ability to use Ethernet for your computer (if that's what you're doing now) or WiFi (which may still have you using a USB adapter or perhaps a card that you install into the computer - not hard).