Not impossible, but not the conventional way to do it and makes it more complex without any advantage.
Li-on has a MAX charge level and gets nasty if much overcharged, or excessively discharged. NiXX simply "tops out" at ~1.5v/cell and the rest is shunted off as heat. As long as the heat is kept at a reasonable level the 'excess' is not much of a problem. You can do this very slowly (old style 15 hour 'dumb' chargers, or more quickly with more modern 'smart' chargers. The smart chargers need to get charge termination correct or they risk over or under charging the pack. A lot of the quality is in the intelligence of the charge termination.
FWIW, charging NiMh correctly is harder than Lithium. But if you get lithium wrong the consequences can be much more severe. I do have some old NiCad drills that the packs died. I replaced them with lithium-ion, no protection and no balancing. I'm pretty careful not to over charge or over discharge. After 3-4 years of occasional use I pulled the pack and put it though a discharge>charge cycle, then tested each cell. I was surprised to find them still in balance.
I built another pack for a weed whacker that is much more demanding, but I didn't have enough high discharge cells for this 24v pack so I paralleled 2 'medium discharge' cells and put this in as a single cell. But that cell has 2x the capacity of the others. It does have a balance tap and it still gets way out of whack with discharge/use. I have to charge it nice and slow, so the charger can deal with balancing it. If I push it too fast the balance mechanism can't keep up.
To Air is Human,
To Respire, Divine.