the supply you have is marginal, but if your utility or the neighbors don't have a problem with it then what's the problem?
200 amps at 240vac is only 48KW.
so i presume you have a pony start on the 40 hp rotary phase converter, and i presume you have the motor run capacitors hooked up to offset its reactive amps, which could be on the order of 30-50 amperes.
meaning, your 40hp motor sucks up on the order of 30-50 amps (almost entirely reactive) from your 200 amp "budget" and almost all of these 30-50 amps can be compensated for with capacitors, which would require on the order of 300-500uF to do so. if you're on a residential service then they don't know about this so its not a problem.. until you read in the fine print where i says something like "up to 5 or 10 hp"
anyhow yes you can just plug your 240 to 480v transformer into your induction motor phase converter, and plug your machine in. how you figure out how to ground the 480v side is up to you, and osha. and you probably want the machine controls on the utility side of your "three phase" so that it gets cleaner power that doesn't brown out when the spindle turns on.
your 25KVA transformer will suck up a few reactive vars, which will push the "generated" leg of your rpc down. you can compensate for this with delta connected capacitors across the transformer.
also, delta connected capacitors at each of your other loads. they should switch out with the loads, not remain permanently connected to the rpc.
while many people permanently connect the capacitors to the rpc, this pushes the voltage of the generated leg far too high and the motor can overheat, or the third phase is high enough voltage to trip a vfd.