Is channeler armor actually imbued with magic?

There is nothing special about Channeller's Set, 'imbued with magic' is just fancy description in this case.

It has relatively high magic defense for it's weight among non-upgradable armor. For example, body armor gives 45 magic resistance and weights 10.1 (so ~4.5 per weight point) while Havel's Armor - 56 and 19.5 ( ~2.8). But that number is not impressive at all - +10 Dingy Robe gives 79.9 MR with weight of 3!

"Imbuing" an item with magic does not always mean that it will have an active effect.

In video games, and especially in Dark Souls, weapons "imbued" with magic are often given an active effect, whereas armour is given a passive effect. In the case of the Chanellers Set, this is its defense rating Vs magic damage.

It is important to point out, however, that Magic resistance is still different to Faith (more specifically Lightning) resistance. While the Chanellers Set might have a good Magic Resistance, it does not do so well against Lightning or Fire.

Interestingly though, while it can't be upgraded, it does have a higher Poison and Bleed resistance than any other Medium armour set, and it is the lightest of all Medium sets, though this comes at the cost of its base defense stats.

http://darksouls.wikia.com/wiki/Channeler%27s_Set