riding on a bent rim

It's really up to you. How bent is it? Without pictures it's hard to say.

Man, don't ride you're awesome racing bike with bent anything.. ..get that RIM replaced ASAP.
I got a friend that does crap like that, and I can hear his poor bike crying out everytime its ridden.. that irritates me something fierce to see a good friend riding his bike when I know it needs a top end, a clutch, brake pads, chain and sprockets, and yes, bent/warped wheels.
Fix it and give your bike the respect it deserves. .its a thoroughbred.

Flat spots in rims are not a big deal, as long as the the rim is true in respect to the hub you will be fine. I use a hydraulic press to get rid of the flat spots. The aluminum that these rims are made out of is pretty malleable and they can have the flat spots pressed out a few times before they crack.

You know better than anyone answering your question what condition your rim is actually in. I see quite a few riders running bent rims beyond the safe limits. I try to steer very clear of such riders. Ask yourself how much are you willing to gamble on it coming apart and know the cost of the damage it could cause to the bike and mostly your health or possibly some inocent rider that might fall victim to your negligent lack of proper maintenance.
That being said, I am currently riding a rim that has a minor flat spot at the rim lock, fairly common on most every bike I've ever owned. You just need to inspect if is "true" and for cracks, loose or broken spokes/nipples, and if it is bent enough that there is a gap between the rim and tire.

Can you true the wheel to help it at all?

No

Riding with some flat spots is not a big deal at all. Unless of course it is a catastrophic dinger

You can't expect anyone to give proper advice with out seeing the part. Take a picture.

The main concern in a flat spot is spoke tension. Without proper spoke tension even on all spokes, the "loose" flat spot area will divert that energy to the tight spokes which can cause failure..

MX wheels don't run on super tight tolerances so you don't have to rocket science the deal, but there is a limit to what is a acceptable flat spot.

replace it, a new rim is cheaper than a trip to the ER.

Naw, just pull the tire off. I've seen people do it with a couple blocks of wood and a sledgehammer.