Your rested EXP is used up by killing mobs (as a battle class), gathering items from a node (as a gathering class), and crafting items (as a crafting class). You will only "gain" rested EXP while crafting in a sanctuary if the rate at which you gain it is outpaced by the rate at which you're making items, which is unlikely. It is not used by completing quests or leves, or by handing in collectibles or GC turnins.
During that interminable period where Best Served With Cold Steel was blocking 99% of players from progressing, I used nearly all of my rested EXP on my miner solely by gathering items. Later, as I was leveling my crafters, I did so again while crafting items, which I usually did at my house, a sanctuary. So, yes, your blue bar will be used by crafting, but perhaps at a lower rate than with the other 2 kinds of classes, since most of your EXP will be gained through turnins.
How much of your rested EXP is taken, I'm not certain. I imagine it's the base amount of EXP you gain from the craft (minus any bonuses from food, FC buffs, manuals, etc) but I couldn't say for sure.
