OK, i'm always the guy who answers these, and then gets stepped on.
I rewound my '05 TE 510 for that years baja 1000. I had Baja Designs do it. Worked with them many times in the past. Best we could get is 12.2 amps at the battery at idle. Thats enough to run dual HID's-which i did, and not draw down the battery at idle. It was a learning exercise for both them and I. I told others raicing Husky in baja, and they followed. Others did the same in following years, and its worked well. I used the stock regulator without issue. Others dont.
Bottom line is we added around 40 watts overall by adding more copper winds, using about all the room there was on the stators pins.
Next year i needed more power for a rallye Husky i was building. I did my homework. Found that a KTM after market stator from Electrosport bolted right into the Husky, with more pins, could put out far more power. Around 300watts total. So i converted to that system, it was trial and error, and after some faulty regulator, and grounding, issues, i got it to work great. Told others about it, and now there are a few Huskys with that set up.
There are a few little tricks to it, but no big deal.
So then out came the '08 bikes with their fuel pumps, very high pressure fuel pumps i might add, and that called for more power.
So on a hunch i ordered an '08 stator for my '07 510, and it bolted right up. Side by side with the original re-wound baja designs stator from '05 it looks IDENTICAL. I mean you couldnt tell which is which.
It too adds about 35-40 watts vs. an '04-'07 stator.
Now--does it have enough extra juice to run heated grips? IN general these bikes do have a bit of extra juice in their electrical budget.
For sure the bike will run fine with heated grips, you will simply be eating into the bikes time needed to re-charge the battery, or worse you will draw down the battery. If you ride high speed, you will probably be fine, if its 40 miles down hill at idle, you might not be able to start the bike at the bottom of the hill, without kicking. Thats one very easy way to find out. And yes, the bike will start with a drained battery. Or you can ride with jumper cables (i do).
If i were you i give it a shot, but first i would replace everything i could with low draw LED's (break light, flashers, rear running, etc), dont run your highbeams, and you will probably just barely be ok. Depends on lots of stuff, like how much draw on the heated grips (new models have variable heat settings, etc), what rev range you ride at, how often you hit the breaks, etc. etc.
Just conserve as much as you can on the rest of the bikes electronics configuration, and you should be fine IMHO. Worst case you have to kick start your bike and turn off the heated grips, and then get a higher output stator. It wont hurt your battery if its in good shape, and you ride and recharge it. Then get the Electrosport high output stator.
I have heated grips on my 610. Love em.

The 610 does have enough extra juice stock to run the grips.
hope that helps/gives ya options.