Can you send texts from iMessage to someone who has Android and uses Handcent?
If you are wondering if the text will be received through Handcent: yes.  If you are wondering if you will get the group text styled messaging from iMessage while using Handcent: no, I don't think you will.  

There are several other SMS options that do support group messaging though.  Android 4.2+ offers group messaging built into the native Messaging app, so if you are on 4.2+ then you probably just need to enable the settting in Messaging app.  If you are on something before 4.2 then you could use GoSMS.  That is what I used until I was updated to 4.2 and it does a great job.  It's not perfect, because Apple likes their iOS exclusivity with iMessage, but it will do the trick.

Again, I am assuming you're looking for a group text solution.  If you are not, disregard my advice.  If you are wondering if Handcent can receive an iMessage, it should, but you wont have a group text to reply to.