Skills will get better when you rank up. It would not make sense if it does not. Rampart for example "increases defense". Now assume that it does not scale with your Gladiator rank. This means that this skill is quite inefficient at rank 33 of your Gladiator (until you get your rank 2 Rampart). At level 34 you get a new rank of the Rampart skill, which will make Rampart I obsolete and probably give you a boost in efficiency. You could also say this for Enmity based skills for example.
If a skill gives you 20 Enmity at level 4. You get a new rank of that skill at level 34. If the skill does not scale with level of class, this skill will give you 20 Enmity at level 33 also, while other classes generate far more Enmity at level 33 then at level 4. This does not make sense so you could conclude that skill does scale with class level. (as far as I know now, Enmity is not based on any attribute).
Also, Physical Level have hidden cap per class level. Based on this, the skill, if you rank up, the hidden cap on your Physical Level will be higher, basically making your skill (which relies on PL) better as you rank up. If this only counts towards your active class remains to be seen and needs testing.
As far as I know and tested this in OB, Skills do get better per level in your class. Either it will be based on PL combined with cap and/or linear based on level of class.
Still this needs more testing to be 100% sure about what skill scales.
I don't think this is what the OP is asking, following your example but directed at what I think the OP question is...
Rampart might work as increases 5% of your Vitality to your Phisical Defense.
As such, everytime you level up (and increase your Vitality) the ammount of defense will increase.
At lvl 33 you get Rampart II which might increase defense by 8% of your Vitality insead of 5%.
Now, directed at OP, If you have rampart on a Conjurer it's efect might be reduced to 3% instead of the original 5%. Abilities, when used in other classes lose some of their efficiency.