Own domain, PHP mail and Google Apps Gmail

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http://serverfault.com – I have a domain thru NameCheap that has no hosting. It has its A-record set to tumblr so the domain points to tumblr's servers. I have all of the MX records set up for Google Apps so I can get mail at my domain that way. I would like buy hosting elsewhere for some server side PHP scripting capability. If I use PHP to send mail with the mail (); function, will it still work with Google Apps? (As a side note, is there a way I can have hosting on a domain but still be able to use Tumblr's backend to display my site, so I can upload scripts? I just have no HTML design talent and like the the (HowTos)