Regardless of whether alcohol combines in a toxic way chemically it doubtless combines in a toxic way generally. Regularly taking alcohol combined with stimulants generally trends to result in worse sober scores on mental focus and ability tests .. though those tests aren't really that useful and the drinkers probably all have hangovers anyway. Also, poor nutrition results in a significant increase in the harmful effects of alcohol .. and regular meth use doubtless produces that. Then there's the fact that you can easily drink a bottle of gin on meth without realising how much your drinking ... and just have slightly wobbly legs. I personally have found no real benefits to a meth high from alcohol just problems during the comedown. It's similar for the H I smoke during a meth run (I generally take only enough to stay well). I've done some crazy dangerous stuff with huge overdoses of fent that worked really well .. but that was only slightly less dangerous than actually attempting suicide from overdose and had a withdrawal at 6 months that was insane.
These days if I take meth .. I just take meth. If you're comboing with meth a lot then I'd suggest you make an effort to think if it's actually worth it. You might have a little twinge every now and again when you think a drink would be nice right now, but you'll forget it quickly and the lack of alcohol will hardly make any difference to the non-comedown experience. I actually like drinking non-alcoholic beer / wine on meth as even though it tastes like shit so does everything on meth and it's the most palatable way I've found to get electrolytes and calories.