I just checked the RCI and Icy Strait Point websites. It looks like the RC-15 excursion is contracted through Icy Strait Point directly. They don't offer it on the ISP website, but I know the ISP folks were looking to hire charter boats out of Juneau to run many of these trips for them. You could end up on any of the locally contracted boats, possibly including some from Juneau... the problem with the brokered ship's excursions is that you really never know who you're going to get (even if you request a boat that you KNOW runs these trips, RCI won't have any clue what or who you're talking about.)
They never have enough boats to keep up with demand, however, so the excursions can't generate too many complaints! If you want to book a charter directly with a local company (so you'll know exactly who you're getting and can talk to them directly beforehand) I'd suggest getting ahold of Floyd (Peterson or Patterson?) at F.I.S.H.E.S. He's a long-time local guide who always gets good reviews. There are several others over there who get quite a bit of press in various discussion forums, but you know how easy it can be to "manipulate" a discussion forum! ;-)
Better not for now... signatures get me banned!