A young white dragon is a tier 2 level boss. Dragons don't tend to be lieutenants or mooks of anyone. At best you get a dragon and a dragon rider as a pair for a mid level threat. But that's just replacing some of the dragon's mooks with the rider. Still a tier 2 threat. A dragon is nobody's mook. They will flee to set up shop somewhere else before submission.
I disagree a bit because we often see young dragons (white or red) in service as pets to frost or fire giants.
In general I agree, but there are certainly cases where dragons are servants and even mooks (for tier 4 and epic games).
Yeah, I get it, but this implies a kind of pre-structured story of a campaign I do not tend to run. I don't have a 12 or 20 level plot the PCs are following that makes this as natural as you are describing. it makes sense in that context, but not in "what's on the random encounter table for CR 6."
So, you don't have ogres as servants to giants? Because that is all the structure is. To be clear, if you don't that's fine of course, just not something I've seen much of.
It isn't about a plot the PCs are following, just the structure of how your game world works. In my world, ogres will serve giants if forced to or enticed into it with promise of carnage and loot. One of my favorite adventure series is Against the Gaints, for example. There, ogres serve giants, and orcs serve as well (but out of fear moreso than respect and will betray the giants if offered their freedom).
I don't know what "random encounter table for CR 6" you mean. For myself, if I roll up a rare encounter, such as hill giants in some areas, I can mix things up by substituting a couple ogres for a hill giant and keep the same rare encounter and to adjust the random difficulty level.
For example, my current party is 8th level. If I roll a random rare encounter and got hill giants, the encounter is designed based on the random difficulty.
Easy: 1 hill giant (1800 xp, maximum for easy)
Moderate: 1 hill giant, 1 ogre (3375 adj. xp)
Hard: 2 hill giants OR 1 hill giant, 2 ogres (5400 adj. xp)
Deadly: 2 hill giants, 1 ogre (8100 adj. xp)
Deadly+: 3 hill giants
A single hill giant is fine for easy, 2 for hard, but if I want moderate or deadly I have to add soemthing, and an ogre lackey or servant fills that role nicely. I might describe the "ogre(s)" as "young hill giants" if I decide, based on the story/world considerations, that ogres would not likely be with giants in the location.