No, I don't think having her face on a motorcycle is objectifying at all. Who says a motorcycle has to be a symbol of masculinity? Lady Gaga has never claimed there to be anything wrong with being 'masculine' or 'feminine' and I think more often than not she makes of point of expressing BOTH just to show that gender roles are so much in our heads.

In the Judas MV she portrays Mary, a strong symbol of femininity, in a motorcycle gang, which is conventionally male. She doesn't play a 'strong female character' in that particular video, but she has portrayed strong women in her music. It just kind of goes to show that to be someone who promotes gender equality you don't have to hoist your gender up as being dominant, it's about being allowed to be any way you want regardless of gender.