Like Scarbucks Coffee mentioned. Rushing guy means getting his frags wherever possible (for free, when theres no better option at that time). Also during survival trial you sometimes get random 1/2//3/4/5/30/80 frags (personally 5* my guy that way, never swept his instances but then again im not using him at all on my fire main). This means just sweeping elite instances. I can't really tell his usefulness for water main, since water main's survivability (at least in higher lvls) is based solely on healing ninjas and shields from ao/mabui. He can be used for ranked battle for sure, since he gives everyone in 3 teams leech based on taijutsu dmg, but havent seen him being used in main team, like ever.

Suigetsu and Haku are ninjas for 9tails/summon fight. Guy can be used here as well, at least until you wont get better ninja (i dont really play water, thats why i cant advice the best, endgame dps team for that main).

As far as refine frags goes: from those you mentioned, kabuto and hinata are the ones that give 10pts/frag, suigetsu gives 5 and guy gives 2. No idea about haku, dont have him 5*. Thats why once you reach 5* on certain ninjas, you only sweep for refining those, which give 10pts, so you get the most value out of your stamina. For more info, search the forum about fragment refining, I remember posting somewhere almost full list of ninjas and how much their frags are worth. There are many topics, not sure if there's one guide containing everything, but you can piece them up to know whats good to farm and whats not.