Any Weapon?

Hi I was just playing and my dervish was able to use a hammer. Can any profession use any weapon?

Any profession is capable of wielding any weapon.
However, unless you have an attribute line for the weapon, you will not get skills for it and you cannot increase the amount of damage you deal with it.

Any class is able to carry any weapon, but unless you have the proper attributes, you can't get the full potential out of it.
For example, the hammer that you used probably required Hammer Mastery to get the full damage out of it. You could, if your secondary was Warrior, put enough attribute points in Hammer Mastery to get full damage.
If you don't have the proper amount and type of attribute points, then the weapon will do only about half damage - or have half the armor rating (shields), or half the energy (focus).
For a caster class, the damage done by the weapon is unimportant since the build usually is based around skills/spells. In this case any weapon that has the features you want, or the skin you like, will do - note though that the requirement for the weapon can affect HCT and HSR mods. This also pertains to a few builds that don't do damage, such as Perma sins (in some cases), runners, tanks, etc.

Any class can and should use a bow for pulling and you don't need any skill points as the idea isn't to damage them so much as split mobs for easy kills.

All other weapons you should really invest skill points into it so really its change your secondary class to the one that usually uses the weapon.

ie Dervish/warrior for hammer.

Primary attributes are what matter.

Any class can wield a sword, but with STRENGTH which govens ARMOR PENETRATION, it is largely futile

This is not strictly true. I refer you to the Requirement, the "drawbacks" section. I don't want to repeat what's on the wiki so read it there. Let's just say that it's a common misconception that the attribute is cut in half, but it's not strictly true.

I said about half damage. I'm aware of the above info, but it really comes under the heading of "picky picky" with regard to the OP's post about using a weapon.