The importance of the foreign volunteers serving the Germans is often greatly overestimated.
For starters, many of the ethnic SS "Divisions" were divisions only in name, they never exceeded regimental strength, and some of them were even smaller.
Secondly, they were nowhere near comparable to the average German infantry units, let alone the lower-numbered large SS units (which by late war were even better equipped than the average Heer Panzer or Panzergrenadier Division). Many of them were poorly equipped and poorly trained, second or third rate units actually. They did come in handy for anti-partisan duties, though that might well become a chicken-egg question; these units were useless as true frontline combat units against regular enemy troops. There were exceptions; a few ethnic SS units had actual regular-combat value. But this was the rule.
Had the Germans recruited more of these men, of course they would have incurred in the obvious difficulty: they were already short on equipment for their own Heer units. Additionally, the foreign manpower pools that had given mid-numbered SS Divisions of some actual frontline combat usefulness had been used; further recruitment drives would have had to rely on those manpower pools that provided the questionable units. So the Germans would have had more second or third rate foot regiments, and they would have still needed to feed, pay, train, arm, clothe and equip them – out of an ever-decreasing resource pool.
Which brings up the usual issue about recruitment drives in the Ukraine and other conquered territories of the USSR. The Germans could have been nicer to Ukrainan city-dwellers. That would have meant, for starters, feeding them. But the regular German Heer units, after 1941, were largely expected to live off the land; the war in the East should have been, ideally, a self-sustaining effort when it came to foodstuffs. Had the Germans chosen to feed the Ukrainan cities, they would have been short on grains (for both men and horses), local transportation means (read horses, wagons and carts) and even strategic transportation means (read rail capacity and rolling stock) which they historically largely sucked up and used to keep their army going. Simultaneously, the German civilian population also was not facing the rationing hardships it would have faced, had food not been stolen from somebody else's farmlands and dinner tables.
The Germans did not choose to largely starve the "superfluous eaters" in Ukraine, and Poland, and Russia etc. simply because they were led by evil racists. One can imagine their leaders being simply mad conquest-seeking imperialists, the problem remains that if they treat their conquered territories nicer, then the pace of their further conquests will not be the one we saw in OTL. And stomachs will grumble back in Berlin too.