Is it possible to connect X-tal load capacitors to Vcc?

As i see it both Vcc and GND have an identical AC potential so there should be no difference. Also, if this holds it should be possible to connect one to VCC and the other to GND. The reason for asking this is that it would simplify board design

I don't think so.
If the Vcc and properly decoupled to GND with 100nF, they could be more or less the same. But a crystal with 22pF should be close to the ATmega chip with the 22pF to GND.

In theory you could use a single capacitor of half the value across the crystal with no
connection to GND or Vcc, since its simply a load capacitor for the crystal, but the
oscillator circuit on the chip may require the usual setup.

Using Vcc instead of GND will inject loads of noise into the oscillator which might play
havoc with the low-power oscillator mode (assuming ground plane and no Vcc plane).
The low-power oscillator on the chip may do special things already to filter out Vcc noise
to allow lower-power operation - or it might not - see if the datasheet says anything on
the matter.

If you're laying out a PCB do it the way that is known to work, unless you want to risk
getting non-functioning board made...

nilton61:
As i see it both Vcc and GND have an identical AC potential so there should be no difference. Also, if this holds it should be possible to connect one to VCC and the other to GND. The reason for asking this is that it would simplify board design

In theory, yes
In practise no
A good board design have a groundplane covering most of one side of the board, just connect it to the groundplane.

Pelle