I could be wrong but do you have to play singleplayer to unlock some characters for multiplayer such as Tai keliso and Dizzy?

I dont know

no

i know that you can unlock characters like Kim and Carmine for Gears 2 if you played certain parts of the Gears of War 1 campaign,
but i dont know about any new characters

Yes you need to play campaign to unlock Tai, Dizzy and Skorge

I believe so.

"Yes you need to play campaign to unlock Tai, Dizzy and Skorge"

well there are others those were just the general ones i could remember, as most people were just saying no or dont know. Was just clarifying there are some characters to be unlocked

playing single player unlocks some characters.

some are unlocked by having achievements from the first game.

edit:

some info from  THIS thread (thanks google)

QUOTE:

"

Cog Unlocks

Tai Kaliso - To unlock Tai Kaliso for use in multiplayer, complete Act 3 in single-player mode on any difficulty.
Dizzy Wallin - To unlock Dizzy Wallin for use in multiplayer, complete Act 1 in single-player mode on any difficulty.
Minh Young Kim - To unlock Lt. Minh Young Kim for use in multiplayer, have the “Time to Remember” achievement on your hard drive from the original Gears of War.
A. Carmine - To unlock Anthony Carmine for use in multiplayer, have any Act 1-related achievements unlocked on your hard drive from the original Gears of War.

Locust Unlocks

Skorge - to unlock Skorge for use in multiplayer, complete Act 5 in single-player mode on any difficulty.
General Raam - To unlock RAAM for use in multiplayer, have the “A Dish Best Served Cold” achievement on your hard drive from the original Gears of War. ( Kill RAAM in GOW1 )
Kantus - To unlock Kantus for use in multiplayer, complete Act 2 in single-player mode on any difficulty.
Flame Drone - To unlock the Flame Grenadier for use in multiplayer, complete Act 4 in single-player mode on any difficulty. (Flame Grenadier may = Flame Drone ? )

"

It's right there on this page.  >.>