Can you send texts from iMessage to someone who has Android and uses Handcent? Can you send texts from iMessage to someone who has Android and uses Handcent?
And if yes does the iPhone user need to have 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.