For the Endor soldiers, Han told them to meet up at the bunker as I recall. That was so they could split up to search for Leia. Since they are at the bunker, they've just been off avoiding Imperial capture I guess, till they could meet up with Han.
What's a better question... Where's the REST of them? There were 3 Dresellian scouts who went along with them, as per the hangar scenes in ROTJ (at least 3 Dresellians are seen walking into the Tyderium, so unless they were just checking out the interior I'd say they went along) and the Shuttle can hold many more troops... It's likely many more went. Enough to fill the shuttle fairly well anyway.
I've always felt those other troops went off looking for another way in, or were sabotaging various areas of the Imperial Garrison on Endor... The various elements of the Imperial base are spread out, so maybe the 2nd commando party was off causing some trouble? They possibly even diverted the Imperial's attention to the main entrance of the power complex? Hard to say for certain, as almost anything's possible.
When Han and the crew are leaving the Tyderium though, there's only a handful of troops following them though, so those other fellows took off somewhere.
As for where Rieekan went, I think I have something for that one. The base had seemingly been evacuated. Since Rieekan was the base commander, he'd be shuffled off immediately. I'd wager he was at the transport site where Luke met up with Rogue Squad to get his X-Wing.
In the game Rogue Leader, the Battle of Hoth is played out in its entirety, sort of... You see the Imperials from their landing zone all the way to their actual 2 fronts.
One front is an assault on the Ion Cannon complex by waves of AT-ST's and infantry which must be taken out first.
The second front is the main trench, and presumably the "North Ridge" where Leia was diverting troops... Also this would be the "hangar" bay, so it makes sense since she said "to protect the fighters" if I am recalling correctly my dialogue...
Leia stuck behind I guess just so a competent leader was there (She would be a morale boost, especially if we follow the EU that says most of the troops at Hoth were Alderaanian nationals who wanted to get some payback). Leia's presence "in charge" would give a morale boost then, but it's also assuming she knows a thing or two about military tactics. By Jedi she's wearing the uniform of some form of Alliance Officer though, and at Hoth she is diverting troops rather forcefully. She may be more than just good at working the Senate floor.
Rikeean though would definately be shuffled off quickly. I'd say one of the transports probably had a heftier fighter cover as a VIP transport of sorts... Maybe it would even be launched just slightly behind 1 or 2 other transports in an attempt to have a decoy screen.
Competent officers with experience are supposedly in short supply for the Alliance though, so they're a valuable commodity.
Where's my damn Rikeean figure? He's too cool to not have a figure yet...