IR Extender Compatible with Motorola VIP 1200

Any extender is just a slave to the IR signals you sent from its RF transmitter to the companion RF receiver that re-emits the IR.  But I don't think your problem lies with that.  All IR extenders are more-or-less the same.  It lies with that cabinet door.  If it's glass then I am not sure any IR blaster is going to get through the glass.  Depends on the glass I suppose.  And of course if it's not even transparent no IR RF receiver/IR blaster is going to get through unless there's room for the IR receiver/blaster to fit behind the door in such a way that the receiver can see the IR.

Then there's the att "point anywhere remote" which has mixed reviews.  It's basically the same as an IR extender/RF transmitter both combined in the remote itself (essentially a S20/S30 remote).  The RF receiver/IR blaster is a USB dongle you plug into the front of the dvr/receiver.  This might work.  I say "might" because, as I said, there are mixed reviews on this remote on Amazon.  Or there was.  I can't even find it on amazon any more.  But that google search I linked to does show other sources.

It's just a IR blaser like any other IR extender recover.  As I said all IR extenders are just slaves relaying the IR codes for the receiver to emit.  So of course it's compatible if the RF signal can be depended on, which I guess is the iffy part of those remotes, and the reason for the reviews it got. 

Note the only reason it plugs into the usb port in the front of the dvr/receiver is because it's near the dvr/receiver IR sensor and also a convenient 5V power source to drive the RF/IR blaster.

There is room in the cabinet for an extender but I need to find out where
the eye is located in the VIP 1200. Which extender do you recommend?

See this thread.  There's many of these IR extenders to choose from.  I don't have a need for them so I can't suggest any one specific model.  Probably most any one you choose will work.  If I were looking for one, for gadgets like this, the first place I would look is Monoprice.com.

It's a receiver (aka set top box, aka STB), not a wifi router.  So has "no band".  And a IR blaster has nothing to do with wifi "frequency" anyhow.

The remotes for Uverse receivers have never been any good.  Too narrow a field and not enough range. 

The way devices like AFTV and AppleTV work using WiFi to carry commands is far better.  I hope the new ATT settop boxes don't use IR.  If they do, I will pass.

I need to train myself to use a phone or tablet app to control the receiver, but it's a hard habit to break.

Should be 36Khz, if I remember correctly.