Can I split the check to 2 Dining programs?
 

I have the business card registered to PC Dining but just registered my SW card for the SW dining. I am taking a friend to dinner tomorrow, it's not going to trigger anything using two different cards for these two programs, right?

As long as the restaurant is okay with your splitting up the charges, it should be okay with Rewards Network. However, you should check both the PC Dining and Southwest Dining sites as, on rare occasion, a restaurant will participate in some programs (partners), but not others.
Relatedly, if you run across a listing for a joint that has a once-per-month earning restriction, that's per partner so a split check between partners there should work okay, too. What you cannot do at those places is split the check on the same card (for additional "elite" requalification credits)! If you did, the one that went through is all you'd be entitled to, period.

I've never had a problem, we've even settled the bar when the table was ready and paid the check after dinner and gotten credit for two visits.

I do it all the time. Sometimes while ordering take out, I order a coke after I have paid for the food. I get one dine for the food and another for the coke. Sometimes I palce all miles in the same dining program other times I earn miles in two different programs. To earn miles in two programs you'll need two different CCs.

As stated above in another post, I also have earned dines for any drinks while waiting for a table.