Warren Buffett isn't an income investor. However, his Berkshire Hathaway (BRK.A -0.33%) (BRK.B -0.20%) portfolio includes plenty of solid dividend stocks, some of which offer especially attractive dividend yields.

But Buffett has positions in more stocks than you'll find in Berkshire's portfolio. Here are three high-yield dividend stocks you probably didn't know Buffett owns.

1. Ares Capital

Ares Capital (ARCC -0.53%) isn't included among the stocks listed in Berkshire's regulatory filings. However, Buffett nonetheless owns a stake in Ares Capital. How? Berkshire's wholly owned subsidiary New England Asset Management (NEAM) holds a position in the stock.

None of the stocks in Berkshire's direct portfolio come close to matching Ares Capital's dividend yield of 10.4%. Ares Capital offers such a high yield because it's a business development company (BDC). Like real estate investment trusts (REITs), BDCs must return at least 90% of their income to shareholders as dividends to avoid paying federal taxes.

But Ares Capital isn't an ordinary BDC. For one thing, it's the largest publicly traded BDC. Ares Capital has also delivered much higher total returns than the S&P BDC Index since its initial public offering in 2004.

I think that Ares Capital just might be the best ultra-high-yield dividend stock on the market right now. The company should have its pick of the most attractive financing deals thanks to the banking crisis. Its stock is also attractively valued, with shares trading below 7.7 times forward earnings.

2. Verizon Communications

Berkshire has directly owned shares of Verizon Communications (VZ 1.01%) in the past. However, Buffett completely exited his position in the telecom giant last year. He remains a Verizon shareholder, though, as a result of NEAM's stake in the company.

Verizon offers an attractive dividend yield of 7.1%. But could that dividend be in trouble? It might seem so based on the company's first-quarter performance: Verizon failed to generate enough free cash flow to cover its dividend.

There's more to the story, though. Verizon's capital expenditures will fall significantly going forward. The company should continue to be in a strong position to fund its dividend at current levels and even extend its streak of 16 consecutive years of dividend increases.

Verizon's growth prospects aren't exciting. That could be a key factor in Buffett's decision to sell Berkshire's shares of the telecom provider. But Verizon still looks like a solid pick for income investors.

3. Viatris

Buffett has had an on-and-off relationship with pharma stocks in recent years. Although Berkshire's portfolio currently includes only one drugmaker (Johnson & Johnson), NEAM owns several. Viatris (VTRS 0.15%) is one of them.

Viatris' dividend yield of over 5.1% ranks as one of the highest yields in the pharma world. Because the company was only formed in 2020 with the merger of Pfizer's Upjohn unit and Mylan, Viatris doesn't have a long dividend track record. 

Wall Street analysts think that the stock could soar. The average 12-month price target for Viatris reflects an upside potential of nearly 60%. One reason for this bullish view is that Viatris is dirt cheap. Its shares trade at only 3.2 times forward earnings.

Could this attractive valuation catch Buffett's eye in the future? Maybe. Even if not, though, Viatris could be just what income investors like: a relatively boring stock with a juicy, steady dividend.