Can you use the PoE ports on your MX for your MR34s? Sure can!
Should you? I would say that depends on your environment and if it makes sense. I would definitely offload wireless to the MR and off the MX. You'll have better functionality and insight for your wireless connections. I currently do not use the PoE on my MX for the access points, but that is only because of physical location, aesthetics, and the fact that I'm using a MS switch with PoE for those and other devices.
I frequently deploy a single MR connected to an MX65 and it works fine. I haven't done two before. I'm not sure what the PoE budget is for an MX65. All the spec sheet says is it has two PoE+ (802.3at) ports - but it doesn't say it has a budget of 60W capable of driving both at the same time.
@PhilipDAth, each port outputs up to 30W of power.
Can do it do 30W on both ports at the same time?
For example, an MS225-48-LP can do 30W on each port - but not all 48 ports at the same time.
Looking at the idle/max load differences between these and the non-PoE MX64s...I can only assume that they can output up to 30W each at the same time. What are your thoughts?
Edit: I haven't tested this as I haven't had the need to as of yet.
That's better. It says it has a budget of 60W meaning it can power both ports at the same time.
As @WadeAlsup eludes to, I wouldn't be using both the wireless from an MX65W appliance and MR devices in the same environment. The MR devices have many more capabilities and you may experience roaming issues, security issues, or more if you have the same SSID configured on the MX65W wireless and the MR devices (and it means you're configuring the wireless in two places too). Best advice is use one or the other not both.