We have 2 small offices, one on each side of a carpark. I can connect the offices using a 2900 in the main office and a 2501 in the 2nd office if the 2nd office is on a different subnet, but I would like both offices to be on the same subnet. My setup is like this:

Main office…
Netgear ADSL Modem Router on 192.168.0.1
Ruckus 2900 on 192.168.0.4

2nd Office…
Ruckus 2501 on 192.168.0.5
Netgear ADSL Modem Router with LAN configured for 192.168.2.x

The cable from the ruckus to the netgear in the 2nd office is plugged into the internet port. It is set up as a DHCP server.

What I want is to have everything on 192.168.0.x is this possible? I have tried just using a switch in the 2nd office but I tend to only get one PC working at a time in this situation. I thought the 2900/2501 would act like a transparent bridge between 2 sites or have I set it up wrongly?

2501 does not have WDS support. What that means is you can not have multiple clients directly connected to its Ethernet port using a hub or switch.
In your setup the Netgear ROUTER is handing out IP addresses and also letting multiple clients connect to the network. There is no alternative to this if you have 2501.

If you have a 2111 then it is a different story. You can have multiple clients connected and they all receive IP address from the main office network. You don’t need another Netgear router in the 2nd office any more.