I think it would be possible to get an AS via arm-tilt, but it should be pretty complicated for several reasons.
The arm swings across the record and therefore the ammount of weight pulling the arm to the side if tilted might vary. Just think of a pendulum. If you swing it up to the top it maybe won´t move at all (down, left or right) as its mass is right above the pivot, or it´ll start moving down slowly at first. If you only move it half way up it´ll fall down quickly as its mass is far away from the pivot.
So a tilted arm also might pull harder and weaker, depending on how far its mass is away from its pivoting point.
Maybe one could use that to achive better AS, as you need more AS at the beginning of the record than at the end anyway, but it might be complicated.
As the mass of the cartridge also does affect the force a tilted arm is pushed by, the tilt of the arm had to be adjusted if you swap a cartridge for another one having a different weight.
Same goes for different tonearms having different mass - and maybe even lenght, as the lenght of the tonearm defines how far the weight of the cartridge is away from the pivoting point (which again should define AS-force).
Adjusting AS also would need a change in the tilt of the arm - and as you need to change AS when you change VTF you´d best need a scaling device for the arm-tilt.
Depending on how far the arm needs to be tilted to achieve the requiered ammount of AS, you may need to consider the effect of the tilt on VTF. Let´s say were tilting the complete tt by 45°. Way too much of course, but easy to imagine. Now if the tt is tilted by 45° only 50% of the VTF would be pushing the stylus into the groove, but the other 50% of VTF would act as an AS-force.
You see that the VTF dialed on the tonearm gets divided into the actual VTF and AS, so you may need to take that into account because you´re loosing in VTF what you gain in AS-force - and in the end the cartridge doesn´t track at, let´s say, 1.5g, but fewer, though 1.5g is dialed in on the tonearm-counterweight.
Apart from that a tilted counterweight also doens´t give all its mass for VTF, so here is also some calculation/compensation requiered to regain the dialed in VTF in real life.
Another thing is most headshells being offset on the tonearm. Now if you tilt the tonearm along its axis, the tilt is pulling the tonearm to the right, but the cartridge is offset which means the cartridge is pulled to the right AND backwards. But as the skating-force is pulling the cartridge to the left only, you want an AS which pulls the cartridge to the right only.
Therefore you´d need to tilt the tonearm in a way so its tilted within the axis of the headshell, not the arm-axis.
And because the arm swings across the record the axis of the cartridge does change a little. Not much but it might result in inconsistent AS.
Last but not least you´d need a reliable way of measuring the ammount of AS your tilted tonearm produces with a certain cartridge (and probably for VTF, too) - because there are a lot of factors going into, so it might be hard to calculate it correct.
Depending on how much the arm needs to be tilted there indeed is a problem in VTA, as ripblade said. If the arm is tilted to the right, the arm-heigth relative to the record does change. From the perspective of the record the arm pivot is higher at the end of the record, than at the beginning.