the majority of it would be active yes (think of the most crude-approach: rubbing crushed pills into a gaping wound. blood is a liquid and more than capable of getting water-soluble compounds from a solid)
(edit: unsure if 'majority', or 'same as if it were fully dissolved'; i'm not seeing the "point of loss", once in the blood there shouldn't be any reason it all dissolves)
re the needle it's possible, it's just a function of particle size, needle gauge, etc etc.
i can imagine there's some potential concerns if it's undissolved (ie, if it needs to become aqueous in the blood(from solid-susp. in your rig), how would you know it was fully-dissolved in blood b4 it was being pumped through your heart? blood is very thick, and you use filters because you certainly don't want solids getting into your bloodstream and being pumped around. If you're depending upon the blood to dissolve a suspended solid, that's obviously very very risky ansd foolish)
mainlining is fun, in large part, because it allows efficiency achieved by removing your body's natural filters. you're talking about approaches where you're removing the accepted standards/safeties of safe-IV'ing. i hope these q's are more theoretical for you, surely you see how dumb it is to play around w/ compounds directly into blood/body w/ liver and other organs processing 1st; removing safeties like filtration or suitable fluid volume (and leaving product undissolved) is foolish at best.