It is always worth learning from another Dom but I am not convinced this needs to be a Domme. Domme's generally (very generally, I admit, as there are many lesbian Dommes out there...) practise on men not women and so would not necessarily understand how to treat a woman (unless, as I said, they were a bi or lesbian Domme...). The techniques and psychology involved are completely different (though there are some similarities). Just to give a few differences off the top of my head:

- differences in emotional and psychological needs
- physical differences in breast and nipple sensitivity (and you can do more with breasts than you can with man boobs)
- Genital differences (need I say more? You can usually hang more weights off a ball sac but you can force a woman to orgasm more...)

He may therefore be better off talking to a male Dom about things this male Dom does to their female subs than talking to a female Domme about male subs. Even if he finds a lesbian/bi Domme, the relationship dynamic is different between a female Domme/female sub and male Dom/female sub (though the techniques will be more or less the same so it may work on that level).

Now, that assumes that all he wants to do is talk... some BDSM practioners beleive that you cannot be a Dom/me unless you have experienced something of being a sub (not necessarily my opinion, not really one I have an opinion on, just reporting what I have seen in various different places). The idea being to get a form of empathy with your sub. If this is what he wants then he may indeed be more comfortable with a female Domme wielding the whip. In fact, he may be wanting to talk to a Domme because he is concerned about male Doms being overbearing and too 'alpha male' for him depsite the fact that this is rarely the case in my experience (most male doms are lovely people and I am not just saying that because they'll whip me if I don't... )

Now, even though I say it may not be directly useful to have a female mentor, I can see no harm in talking to as many Dom/mes and subs as you can to get a good feel for the lifestyle as a whole. Mentoring, however, is a more direct 'this is how I do things, now you try it' sort of relationship which means there may be clashes in technique.