/me grins. Hey Bear!
Okay, so I'm one of these women that alts a FW and slave in the same sim. For me, personally, there are no OOC feelings invested in my character, at all. I try to be as clear about this as I can. I always set out that I would love to get along with people OOC, become friends, whatever, but there will never, ever, ever be anything more. Ever. Just to drive that point home, it's ALWAYS a big concern of mine and ALWAYS made clear when I roleplay with someone. So in my opinion, with that made clear in a roleplay genre that is exclusively for adults, the 'feelings' thing shouldn't be a problem. If I get a hint that it is potentially a problem, I will engineer a way to get away, and stay away, from the said person, regardless of which character I'm roleplaying.
OOC communication is key to good, intense roleplay in my opinion. I want to be able to roleplay my characters being head over heels in love with character X IC, or detesting character Y, or insulting character Z(no wait, let's just call her Allison <3)'s dress without OOC drama, in a way that lets us both immerse in the story and run with being creative, rather than getting all stuffy about 'OMG are you insulting me/in love with me/ hate me OOCly?!'. So yeah, my point there, just to make it absolutely clear, is that I don't do OOC, and if something is a potential "ew" point, where one of my characters is gonna get pissed, then I'll drop an IM along the lines of "My character is gonna get real pissy about that. I'm just letting you know there's no OOC Malice". As strongly as I separate IC/OOC, I separate my characters. My slave will NEVER be pissy at the same character my FW is pissy at, unless she has her own IC reasons to be. Same thing goes with anything else. If and when I roleplay with someone I have potential to see on both characters, which for me is quite a lot, I use the 'notes' box in their profile so I don't get muddled up about what interactions have gone before, on which toon.
I am incredibly lucky, in that I roleplay with an amazing bunch of people who 'get' the difference between IC and OOC. Most (if not all) of them know who my two characters are, and that they're both played by me. I've no reason to hide that fact from them, because again, they're very adept at grasping the basic principles of IC/OOC, and I can only assume that they've seen me play both my characters, realised that there is no potential for drama, and simply treated them as different entities (as they should). If someone tried talking to me on one character about something that had happened on the other, they would receive a polite IM to tell them that they needed to address the right character.
That said, I don't use my alts to escape IC drama or punishment on the other. It's rare that such rich opportunities for character building or storyline creation come up, so when they do I'm all over them like glue. My slave character was recently bought by someone in a different time zone, she then got stolen, and is consequently (since her return) being kept chained to her owner's side or bed. which is fine, it's character building. It's storyline. I love it. BUT - I'm not going to sit around staring at the walls of a room and roelplay sleeping, or being chained to a post, by myself. I will certainly roleplay the necessary feelings that surround that during the times that he is on for me to roleplay with him. But when he's offline? I'm on my alt.
I write a lot outside of SL. Character creation and storymaking have become second nature to me, but the thrill of having someone else's imagination and input to feed off of keeps me coming back to RP every day. So as much as I can write a story about (eg) a bored 40-something male cab driver, or a suicidal teenage girl, without crossing their stories over, I can write one about a slave and a free woman, separately, without crossing their stories.
My characters are totally different from each other. They are not involved in each other's storylines even though they're in the same sim, they do not resemble each other in any way, and I am always, if asked, honest about who my alt is. Sometimes even if I'm not asked!
In summation, I would say if you're confident that you can separate IC/OOC AND your both (or more) characters enough that you will not cause any drama, go for it. If there is even the tiniest chance that you will be unable to separate completely, even if that just means the tiniest little one pixel blur of a line, then steer clear because it'll make you a ticking dramabomb.