Yea, I actually had a HUGE PROBLEM trying to get a female ledian when I had my female Delcatty in the front, so I'm pretty sure this is true. However, I dunno if this will even out the odds for rarer type genders...
*should go try with togepi* In any case, I don't see how pokemon mansion would be any different. :V
I have a female Eevee if you want one :V