Technically, having one account with receivers at 2 separate homes is a violation of the Customer Agreement. But, just like I like to say about the speed limit, "it's only illegal if you get caught".
Here is the relevant section from the
Customer Agreement for those that care:
Section 1(f):
Phone Connections. For optimal performance of your Receiving Equipment, including ordering with your remote control or receiving certain Services, each of your receivers must be directly connected to the same land-based telephone line. If you add Service on additional TVs, you may purchase a separate subscription for each additional TV, or, if all your receivers are continuously connected to the same land-based telephone line, we can "mirror" programming to your additional TVs and charge you only the fee amount described in Section 2. You agree to provide true and accurate information about the location of your receivers. If we detect that any receiver is not regularly connected to a land-based telephone line, we may investigate and, if it is determined that the receiver is not at the location identified on your account, we may disconnect the receiver or charge you the full programming subscription price for the receiver.
That section is quite clear: if your receivers aren't connected to the same land-based phone line, DirecTV can charge you full subscription price for each receiver, instead of only paying the mirroring/lease fee for additional recievers.
Since "land-based phone line" means the old POTS* lines, it isn't possible to have the same phone number at 2 different locations. Therefore, this phone line rule excludes having multiple locations on the same account.
It is well known, though, that DirecTV doesn't actively enforce the phone line requirement anymore, and typically only uses it to bust the big fraudsters.
In my many years as a DirecTV employee, I only heard of a few times where people were busted for having multiple homes on the same account, and those were usually the idiots that were reselling service to their neighbors and had
lots of receivers on their account.
* For those that don't know, "POTS" = "Plain Old Telephone Service", i.e. not cell service, satellite phone, VOIP, etc, just your plain old boring basic dial tone phone service.