That'd be awesome. Except they would probably have to use the terminals to do it, since most of the general populace doesn't know how they got in the Dyson Sphere in the first place.

im assuming those three distant spartans are grey team- but were they at the fall of reach?

if the other spartans show up in halo 3- 12 year old super gamers from texas will flip thginking osmeone cloned the mc- but first those other spartans need to get themselves out of the dyson sphere, nothing has indicated they got a help message out to anyone, or anyone is going to look for them

but if they do show up in h3- that would be uber dope

True, it would make no sense at all if more spartans showed up, but we've had wierder things happe. To someone who hasn't read the book, Johnson was standing RIGHT NEXT TO the PoA when it blew, and somehow magically apeared on the Ciaro in H2. (PS, I have read the book, and I still have trouble figuring out how Sgt J managed to hitch a ride on the pelican before the ring blew). If bungie wanted, they could be brought back. I can see it now:
"Hiya chief"
"WTF are you doing here?"
"Long story."
"I won't ask then. Pick up a gun and help."
It's unlikely though. I can't see an effective way to slip them into the events as seen without book assistance.

well, johnson was in h2 and not many people asked questions, but throwing the other sparatsn in would be confusing to those who never heard of the books