TL;DR
Call the "workstation group". They have a direct line 1-877-671-3355 and are knowledgeable about the Ubuntu laptops that DELL sells.
They will help you directly if you have a hardware issue. If it is a software issue, they will open a ticket with special support that (I was told) has no direct line and they will call you back directly.
Don't call 1-800-999-3355 for Ubuntu laptops
Every time I call them, I get asked to call 1-866-982-8688. This number gives 2 options - to be connected with Ubuntu Advantage (which owning a DELL laptop does not entitle you to) or DELL DataSafe. Selecting DataSafe instructs you to call 1-877-218-1671. The techs there cannot support DELL laptops and will redirect you. I tried explaining this to the technicians at 1-800-999-3355, but they continued to insist I call the 1-866-982-8688 number.
UPDATE: I recently just called the 1-877-671-3355 and was instructed to call the 8688 number again. If DELL suggests that you call that number, inform them that it doesn't work. Hopefully they can look into this and get it sorted out internally.
UPDATE AGAIN: After much difficulty with DELL regarding Linux support, I remain very skeptical that the technicians or representative I speak to can accurately represent the Linux experience with DELL. For example, they may tell you that you can do something (such as use a DELL diagnostic tool or recommend updating drivers) with Windows, that simply isn't possible or sensical using Linux. I am very disappointed with this experience from DELL. I would not recommend it. DELL has technicians capable of supporting Linux, but chances are you wont get to speak with them or replies will be significantly delayed.
Be careful when speaking with DELL's sales especially.