Is it safe to run bitcoind on another server I'm making first, rough concepts of some ideas for bitcoin-enabled services I have in mind.

One thing that I wonder is, is there a best-practise approach on running bitcoind on another server that acts as backend for a particular other server?

I thought of something like that:

I have a vServer A and a plain and simple PHP-Webspace at another host B.

A runs my bitcoind-deamon and only allows RPC-calls from Bs IP.

B makes its RPC-calls to A in a server-proccess which was not triggered by a client/website-visitor.

How safe would you ensure such a scenario? Is it possible that nodes, connected to my vServer A, identify the servers purpose from the transactions and try to attack him?

Even if they do, they would have to use a MiM-attack, because A only accepts Bs IP.

What else can I do to make the communication more secure? HTTP-Auth, SSL?
If you have SSH access on both machines you can simply create an SSH tunnel from machine B to A and forward port 8332 through it. That way the behavior is just like it would be if bitcoind were installed on both machines, the traffic between the two machines is encrypted with SSH and bitcoind does only have to listen to the loopback interface and would not be accessible from the network.