Schutzen motorized recce command

Schutzen motorized recce command has 3 men in sdkfz.250/10. They can disembark from wehicle or they are bound to gun as crew?

They can disembark...

German 251 half-tracks had a designated gunner and driver, and while perhaps in reality you may be disembarking the gun team from the 250/10, it can still drive as in real life it had a four man crew. 

It's up to you if you want to allow it to fire as well, but it seems perhaps unlikely if they have got out.

In the case of the 250/10 you are disembarking the officer and two scouts leaving only the driver in the vehicle. 

They don't have a designated gun team as well like the 251s tended to have their own driver and gunner team (when resources allowed).

Are these three armed with an mg34 or just rifle's ?

The game assumes there are always enough crew for a vehicle to do whatever it needs to in the game (move and fire generally), as part of the vehicle (and cannot dismount). It doesn't worry about who gets left behind to do what, etc...  here,the 3 men can get out, and as the recce HQ, I doubt they have an MG34 -if it doesn't say so, (no book to hand), then no.