Is it possible to connect different forms to different merchant accounts?

We would like to set up multiple donation forms on our site, each for a different nonprofit partner. I'm not seeing a way to do that - it looks like only one gateway can be set up. Is that correct? I hope I'm missing something.

The GF Authorize.net ADD-ON can only connect to one Authorize.net account. But you can still use the GravityForms PLUGIN to create forms that connect to different AuthNet accounts -- by handling the AuthNet part yourself, with custom api code in your functions.php, instead of using the GF AuthNet Add-on.

Right. I haven't actually tried using different Authorize.net accounts in a single wp site. But the code from that forum post (actually in http://pastebin.com/4QU5HeWD) contains the AuthNet account credentials:

# CONFIG
                # todo secure these creds better!
                # todo change for prod
        define("AUTHORIZENET_API_LOGIN_ID", "xxxxxxxx"); // enter YOURS
        define("AUTHORIZENET_TRANSACTION_KEY", "xxxxxxxxxxx");  // enter YOURS
        define("AUTHORIZENET_SANDBOX", true); //dev: true
        define("TEST_REQUEST", "FALSE");  // You may want to set to true if testing against production

So I would think you could just use different credentials there, based on whatever conditions you might have. As the comments in the code show, though, you might want to secure those values better, in a config file or something, perhaps outside the doc-root, with stronger htaccess restrictions, etc. I haven't gotten around to that step for my own site yet.