OK...I'll wade in. First of all you can mill with a drill chuck without hurting your machine. Here is what to consider and be aware of.
1 A quick tightening (without a key) is a no no. Use the smallest key locking chuck you have only.
2 Use 1/4 the speed and feeds. Depth of cuts cannot be very much maybe 20% of the diameter of the cutter max. That's max!
3 Exspect it to have some chatter. think about the small size spindles those machines have. That goes for later, after you get your cutters, keep them as close to the spindle as you can.
4 The cutters will runout a lot and cut more on one side than the other and you may not get a good a finish.
So...some slight risk to the spindle if your not careful...poor finish maybe...chattering most likely
I suggest slowwww starting with .01 deep cuts...with chatter increase...the feed rates.
Have fun... use a little cutting oil or wd-40... dab on with a small brush... that will help slightly.
It's your machine...I'm just saying how I would do it if I had your size of machine.